Revert DSP-23657 (#1765)

This reverts commit 229854b due to test
failures in cndb.

Author: szymon-miezal

src/java/org/apache/cassandra/cache/ChunkCache.java

@@ -549,7 +549,7 @@ public SingleRegionChunk(long offset, ByteBuffer buffer)
         public ByteBuffer buffer()
         {
             assert isReferenced() : "Already unreferenced";
-            return buffer.duplicate().limit(bytesRead);
+            return buffer.duplicate();
         }
 
         public long offset()
@@ -689,12 +689,6 @@ public void invalidateIfCached(long position)
             synchronousCache.invalidate(new Key(readerId, pageAlignedPos));
         }
 
-        @Override
-        public long adjustPosition(long position)
-        {
-            return source.adjustPosition(position);
-        }
-
         @Override
         public void close()
         {