Remove extra parenthesis from comment.

src/backend/storage/ipc/procarray.c

@@ -2127,7 +2127,7 @@ GetSnapshotDataReuse(Snapshot snapshot)
 	 * GetSnapshotData() cannot change while ProcArrayLock is held. Snapshot
 	 * contents only depend on transactions with xids and xactCompletionCount
 	 * is incremented whenever a transaction with an xid finishes (while
-	 * holding ProcArrayLock) exclusively). Thus the xactCompletionCount check
+	 * holding ProcArrayLock exclusively). Thus the xactCompletionCount check
 	 * ensures we would detect if the snapshot would have changed.
 	 *
 	 * As the snapshot contents are the same as it was before, it is safe to