Revert "Bumping 2.x to 2.6 (opensearch-project#5744)"

This reverts commit 06c1712.

.ci/bwcVersions

@@ -45,7 +45,6 @@ BWC_VERSION:
   - "1.3.6"
   - "1.3.7"
   - "1.3.8"
-  - "1.3.9"
   - "2.0.0"
   - "2.0.1"
   - "2.0.2"
@@ -59,6 +58,3 @@ BWC_VERSION:
   - "2.4.0"
   - "2.4.1"
   - "2.4.2"
-  - "2.5.0"
-  - "2.5.1"
-  - "2.6.0"

buildSrc/version.properties

@@ -1,4 +1,4 @@
-opensearch        = 2.6.0
+opensearch        = 2.5.0
 lucene            = 9.4.2
 
 bundled_jdk_vendor = adoptium

server/src/main/java/org/opensearch/Version.java

@@ -106,9 +106,7 @@ public class Version implements Comparable<Version>, ToXContentFragment {
     public static final Version V_2_4_1 = new Version(2040199, org.apache.lucene.util.Version.LUCENE_9_4_2);
     public static final Version V_2_4_2 = new Version(2040299, org.apache.lucene.util.Version.LUCENE_9_4_2);
     public static final Version V_2_5_0 = new Version(2050099, org.apache.lucene.util.Version.LUCENE_9_4_2);
-    public static final Version V_2_5_1 = new Version(2050199, org.apache.lucene.util.Version.LUCENE_9_4_2);
-    public static final Version V_2_6_0 = new Version(2060099, org.apache.lucene.util.Version.LUCENE_9_4_2);
-    public static final Version CURRENT = V_2_6_0;
+    public static final Version CURRENT = V_2_5_0;
 
     public static Version readVersion(StreamInput in) throws IOException {
         return fromId(in.readVInt());