Clean up code with NET8_0_OR_GREATER

src/libraries/System.Collections/src/System/Collections/Generic/OrderedDictionary.cs

@@ -6,7 +6,7 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
-#if NET8_0_OR_GREATER
+#if NET
 using static System.ArgumentNullException;
 using static System.ArgumentOutOfRangeException;
 #else

src/libraries/System.Collections/src/System/Collections/ThrowHelper.cs

@@ -34,7 +34,7 @@ internal static void ThrowIndexArgumentOutOfRange() =>
         internal static void ThrowVersionCheckFailed() =>
             throw new InvalidOperationException(SR.InvalidOperation_EnumFailedVersion);
 
-#if !NET8_0_OR_GREATER
+#if !NET
         /// <summary>Throws an <see cref="ArgumentNullException"/> if <paramref name="argument"/> is null.</summary>
         /// <param name="argument">The reference type argument to validate as non-null.</param>
         /// <param name="paramName">The name of the parameter with which <paramref name="argument"/> corresponds.</param>

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/ZLibException.cs

@@ -53,20 +53,16 @@ public ZLibException(string? message, Exception? innerException) : base(message,
         /// </summary>
         /// <param name="info">The SerializationInfo that holds the serialized object data about the exception being thrown.</param>
         /// <param name="context">The StreamingContext that contains contextual information about the source or destination.</param>
-#if NET8_0_OR_GREATER
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
         [EditorBrowsable(EditorBrowsableState.Never)]
-#endif
         protected ZLibException(SerializationInfo info, StreamingContext context) : base(info, context)
         {
             _zlibErrorContext = info.GetString("zlibErrorContext");
             _zlibErrorCode = (ZLibNative.ErrorCode)info.GetInt32("zlibErrorCode");
             _zlibErrorMessage = info.GetString("zlibErrorMessage");
         }
 
-#if NET8_0_OR_GREATER
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
-#endif
         void ISerializable.GetObjectData(SerializationInfo si, StreamingContext context)
         {
             base.GetObjectData(si, context);

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ICollectionDebugView.cs

@@ -11,14 +11,7 @@
 
         public ICollectionDebugView(ICollection<T> collection)
         {
-#if NET8_0_OR_GREATER
             ArgumentNullException.ThrowIfNull(collection);
-#else
-            if (collection is null)
-            {
-                throw new ArgumentNullException(nameof(collection));
-            }
-#endif
 
             _collection = collection;
         }

src/libraries/System.Private.CoreLib/src/System/Collections/ObjectModel/CollectionHelpers.cs

@@ -9,15 +9,7 @@
     {
         internal static void ValidateCopyToArguments(int sourceCount, Array array, int index)
         {
-#if NET8_0_OR_GREATER
             ArgumentNullException.ThrowIfNull(array);
-#else
-            if (array is null)
-            {
-                throw new ArgumentNullException(nameof(array));
-            }
-#endif
-
             if (array.Rank != 1)
             {
                 throw new ArgumentException(SR.Arg_RankMultiDimNotSupported, nameof(array));
@@ -28,15 +20,8 @@
                 throw new ArgumentException(SR.Arg_NonZeroLowerBound, nameof(array));
             }
 
-#if NET8_0_OR_GREATER
             ArgumentOutOfRangeException.ThrowIfNegative(index);
             ArgumentOutOfRangeException.ThrowIfGreaterThan(index, array.Length);
-#else
-            if (index < 0 || index > array.Length)
-            {
-                throw new ArgumentOutOfRangeException(nameof(index));
-            }
-#endif
 
             if (array.Length - index < sourceCount)
             {

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCharClass.cs

@@ -1042,7 +1042,7 @@ public static bool ParticipatesInCaseConversion(ReadOnlySpan<char> s)
         /// <summary>Gets whether the specified span contains only ASCII.</summary>
         public static bool IsAscii(ReadOnlySpan<char> s)
         {
-#if NET8_0_OR_GREATER
+#if NET
             return Ascii.IsValid(s);
 #else
             foreach (char c in s)

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexParser.cs

@@ -1938,7 +1938,7 @@ internal static int MapCaptureNumber(int capnum, Hashtable? caps) =>
                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, Q, S, 0, 0, 0
         ];
 
-#if NET8_0_OR_GREATER
+#if NET
         private static readonly SearchValues<char> s_metachars =
             SearchValues.Create("\t\n\f\r #$()*+.?[\\^{|");