Fix duplicate words in comments

Remove accidentally duplicated words in code comments.

Author: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://postgr.es/m/87bl45t0co.fsf@wibble.ilmari.org

src/backend/storage/buffer/bufmgr.c

@@ -666,7 +666,7 @@ ReadRecentBuffer(RelFileNode rnode, ForkNumber forkNum, BlockNumber blockNum,
 		{
 			/*
 			 * It's now safe to pin the buffer.  We can't pin first and ask
-			 * questions later, because because it might confuse code paths
+			 * questions later, because it might confuse code paths
 			 * like InvalidateBuffer() if we pinned a random non-matching
 			 * buffer.
 			 */

src/backend/storage/ipc/standby.c

@@ -130,7 +130,7 @@ InitRecoveryTransactionEnvironment(void)
  *
  * This must be called even in shutdown of startup process if transaction
  * tracking has been initialized. Otherwise some locks the tracked
- * transactions were holding will not be released and and may interfere with
+ * transactions were holding will not be released and may interfere with
  * the processes still running (but will exit soon later) at the exit of
  * startup process.
  */