Fix assorted inconsistencies.

There were a number of issues in the recent commits which include typos,
code and comments mismatch, leftover function declarations.  Fix them.

Reported-by: Alexander Lakhin
Author: Alexander Lakhin, Amit Kapila and Amit Langote
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/ef0c0232-0c1d-3a35-63d4-0ebd06e31387@gmail.com

src/backend/access/transam/xact.c

@@ -91,8 +91,8 @@ int			synchronous_commit = SYNCHRONOUS_COMMIT_ON;
  * need to return the same answers in the parallel worker as they would have
  * in the user backend, so we need some additional bookkeeping.
  *
- * XactTopTransactionId stores the XID of our toplevel transaction, which
- * will be the same as TopTransactionState.transactionId in an ordinary
+ * XactTopFullTransactionId stores the XID of our toplevel transaction, which
+ * will be the same as TopTransactionState.fullTransactionId in an ordinary
  * backend; but in a parallel backend, which does not have the entire
  * transaction state, it will instead be copied from the backend that started
  * the parallel operation.

src/backend/access/transam/xlog.c

@@ -314,8 +314,6 @@ static bool recoveryStopAfter;
  *
  * recoveryTargetTLI: the currently understood target timeline; changes
  *
- * recoveryTargetIsLatest: was the requested target timeline 'latest'?
- *
  * expectedTLEs: a list of TimeLineHistoryEntries for recoveryTargetTLI and the timelines of
  * its known parents, newest first (so recoveryTargetTLI is always the
  * first list member).  Only these TLIs are expected to be seen in the WAL

src/backend/access/transam/xloginsert.c

@@ -1024,7 +1024,7 @@ log_newpage_buffer(Buffer buffer, bool page_std)
 /*
  * WAL-log a range of blocks in a relation.
  *
- * An image of all pages with block numbers 'startblk' <= X < 'endblock' is
+ * An image of all pages with block numbers 'startblk' <= X < 'endblk' is
  * written to the WAL. If the range is large, this is done in multiple WAL
  * records.
  *