Fix inconsistencies and typos in the tree, take 10

This addresses some issues with unnecessary code comments, fixes various
typos in docs and comments, and removes some orphaned structures and
definitions.

Author: Alexander Lakhin
Discussion: https://postgr.es/m/9aabc775-5494-b372-8bcb-4dfc0bd37c68@gmail.com

src/backend/port/posix_sema.c

@@ -189,7 +189,7 @@ PGSemaphoreShmemSize(int maxSemas)
  * maxSemas parameter is just used to size the arrays.  For unnamed
  * semaphores, there is an array of PGSemaphoreData structs in shared memory.
  * For named semaphores, we keep a postmaster-local array of sem_t pointers,
- * which we use for releasing the semphores when done.
+ * which we use for releasing the semaphores when done.
  * (This design minimizes the dependency of postmaster shutdown on the
  * contents of shared memory, which a failed backend might have clobbered.
  * We can't do much about the possibility of sem_destroy() crashing, but

src/backend/port/win32/signal.c

@@ -102,7 +102,7 @@ pgwin32_signal_initialize(void)
 /*
  * Dispatch all signals currently queued and not blocked
  * Blocked signals are ignored, and will be fired at the time of
- * the sigsetmask() call.
+ * the pqsigsetmask() call.
  */
 void
 pgwin32_dispatch_queued_signals(void)