Remove invalid NameResolution tests (#24147)

The Dns_GetHostEntryAsync_* are fundamentially invalid because it's
possible for the broadcast address, 255.255.255.255, to have an DNS
mapping via manually modifying the hosts file.  This was actually
happening on Mac systems as well as an virtual environment running on
top of that (i.e. Windows on Parallels).

Ref:
https://github.com/dotnet/corefx/issues/23992#issuecomment-330250642

Contributes to #23992

src/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs

@@ -91,34 +91,6 @@ public async Task Dns_GetHostEntryAsync_AnyIPAddress_Fail(IPAddress address)
             await Assert.ThrowsAsync<ArgumentException>(() => Dns.GetHostEntryAsync(addressString));
         }
 
-        public static IEnumerable<object[]> GetNoneAddresses()
-        {
-            yield return new object[] { IPAddress.None };
-        }
-
-        [PlatformSpecific(~TestPlatforms.OSX)] // macOS will resolve IPAddress.None to broadcasthost and produce a valid listing
-        [Theory]
-        [MemberData(nameof(GetNoneAddresses))]
-        public async Task Dns_GetHostEntryAsync_NoneIPAddress_Fail(IPAddress address)
-        {
-            string addressString = address.ToString();
-
-            await Assert.ThrowsAnyAsync<SocketException>(() => Dns.GetHostEntryAsync(address));
-            await Assert.ThrowsAnyAsync<SocketException>(() => Dns.GetHostEntryAsync(addressString));
-        }
-
-        [PlatformSpecific(TestPlatforms.OSX)] // macOS will resolve IPAddress.None to broadcasthost and produce a valid listing
-        [Theory]
-        [MemberData(nameof(GetNoneAddresses))]
-        public async Task Dns_GetHostEntryAsync_NoneIPAddress_Success(IPAddress address)
-        {
-            IPHostEntry result = await Dns.GetHostEntryAsync(address);
-            Assert.NotNull(result);
-            Assert.NotNull(result.AddressList);
-            Assert.Equal(1, result.AddressList.Length);
-            Assert.Equal(address, result.AddressList[0]);
-        }
-
         [Fact]
         public void DnsBeginGetHostEntry_BadName_Throws()
         {