Fix typos.

Author: Hou Zhijie
Discussion: https://postgr.es/m/855a9421839d402b8b351d273c89a8f8@G08CNEXMBPEKD05.g08.fujitsu.local

src/backend/storage/ipc/procarray.c

@@ -1600,7 +1600,7 @@ TransactionIdIsActive(TransactionId xid)
  * See the definition of ComputedXidHorizonsResult for the various computed
  * horizons.
  *
- * For VACUUM separate horizons (used to to decide which deleted tuples must
+ * For VACUUM separate horizons (used to decide which deleted tuples must
  * be preserved), for shared and non-shared tables are computed.  For shared
  * relations backends in all databases must be considered, but for non-shared
  * relations that's not required, since only backends in my own database could

src/include/access/xlogreader.h

@@ -17,7 +17,7 @@
  *		XLogBeginRead() or XLogFindNextRecord(), and call XLogReadRecord()
  *		until it returns NULL.
  *
- *		Callers supply a page_read callback if they want to to call
+ *		Callers supply a page_read callback if they want to call
  *		XLogReadRecord or XLogFindNextRecord; it can be passed in as NULL
  *		otherwise.  The WALRead function can be used as a helper to write
  *		page_read callbacks, but it is not mandatory; callers that use it,