Revert "Logical decoding of sequences"

This reverts a sequence of commits, implementing features related to
logical decoding and replication of sequences:

 - 0da92dc530
 - 80901b3291
 - b779d7d8fd
 - d5ed9da41d
 - a180c2b34d
 - 75b1521dae
 - 2d2232933b
 - 002c9dd97a
 - 05843b1aa4

The implementation has issues, mostly due to combining transactional and
non-transactional behavior of sequences. It's not clear how this could
be fixed, but it'll require reworking significant part of the patch.

Discussion: https://postgr.es/m/95345a19-d508-63d1-860a-f5c2f41e8d40@enterprisedb.com

src/backend/executor/execReplication.c

@@ -649,9 +649,7 @@ void
 CheckSubscriptionRelkind(char relkind, const char *nspname,
 						 const char *relname)
 {
-	if (relkind != RELKIND_RELATION &&
-		relkind != RELKIND_PARTITIONED_TABLE &&
-		relkind != RELKIND_SEQUENCE)
+	if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("cannot use relation \"%s.%s\" as logical replication target",