Drop deprecated gucs mechanism

This commit gets rid of the deprecated GUCs mechanism, thereby rendering
the old `set_user.superuser_whitelist` GUC useless.

Users should update their postgresql.conf to use the newer
`superuser_allowlist`.

set_user.c

@@ -55,7 +55,6 @@
 PG_MODULE_MAGIC;
 
 #include "compatibility.h"
-#include "deprecated_gucs.h"
 
 #define ALLOWLIST_WILDCARD	"*"
 #define SUPERUSER_AUDIT_TAG	"AUDIT"
@@ -103,9 +102,6 @@ extern Datum set_user(PG_FUNCTION_ARGS);
 void _PG_init(void);
 void _PG_fini(void);
 
-DEPRECATED_GUC(nosuperuser_target_whitelist, nosuperuser_target_allowlist, NOSU_TargetWhitelist, NOSU_TargetAllowlist)
-DEPRECATED_GUC(superuser_whitelist, superuser_allowlist, SU_Whitelist, SU_Allowlist)
-
 /* used to block set_config() */
 static void set_user_object_access(ObjectAccessType access, Oid classId, Oid objectId, int subId, void *arg);
 static void set_user_block_set_config(Oid functionId);
@@ -532,9 +528,6 @@ _PG_init(void)
 							 NULL, &exit_on_error, true, PGC_SIGHUP,
 							 0, NULL, NULL, NULL);
 
-	DefineDeprecatedStringVariable(nosuperuser_target_whitelist, nosuperuser_target_allowlist, NOSU_TargetWhitelist, NOSU_TargetAllowlist);
-	DefineDeprecatedStringVariable(superuser_whitelist, superuser_allowlist, SU_Whitelist, SU_Allowlist);
-
 	/* Install hook */
 	prev_hook = ProcessUtility_hook;
 	ProcessUtility_hook = PU_hook;