Remove unused typedefs

There were a few typedefs that were never used to define a variable or
field.  This had the effect that the buildfarm's typedefs.list would
not include them, and so they would need to be re-added manually to
keep the overall pgindent result perfectly clean.

We can easily get rid of these typedefs to avoid the issue.  In a few
cases, we just let the enum or struct stand on its own without a
typedef around it.  In one case, an enum was abused to define flag
bits; that's better done with macro definitions.

This fixes all the remaining issues with missing entries in the
buildfarm's typedefs.list.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/1919000.1715815925@sss.pgh.pa.us

src/backend/commands/async.c

@@ -396,10 +396,10 @@ typedef struct NotificationList
 
 #define MIN_HASHABLE_NOTIFIES 16	/* threshold to build hashtab */
 
-typedef struct NotificationHash
+struct NotificationHash
 {
 	Notification *event;		/* => the actual Notification struct */
-} NotificationHash;
+};
 
 static NotificationList *pendingNotifies = NULL;
 
@@ -2299,7 +2299,7 @@ AddEventToPendingNotifies(Notification *n)
 
 		/* Create the hash table */
 		hash_ctl.keysize = sizeof(Notification *);
-		hash_ctl.entrysize = sizeof(NotificationHash);
+		hash_ctl.entrysize = sizeof(struct NotificationHash);
 		hash_ctl.hash = notification_hash;
 		hash_ctl.match = notification_match;
 		hash_ctl.hcxt = CurTransactionContext;