Don't handle PUBLIC/NONE separately

Since those role specifiers are checked in the grammar, there's no need
for the old checks to remain in place after 31eae6028e.  Remove them.

Backpatch to 9.5.

Noted and patch by Jeevan Chalke

src/backend/commands/user.c

@@ -311,13 +311,6 @@ CreateRole(CreateRoleStmt *stmt)
 					 errmsg("permission denied to create role")));
 	}
 
-	if (strcmp(stmt->role, "public") == 0 ||
-		strcmp(stmt->role, "none") == 0)
-		ereport(ERROR,
-				(errcode(ERRCODE_RESERVED_NAME),
-				 errmsg("role name \"%s\" is reserved",
-						stmt->role)));
-
 	/*
 	 * Check the pg_authid relation to be certain the role doesn't already
 	 * exist.
@@ -1159,13 +1152,6 @@ RenameRole(const char *oldname, const char *newname)
 				(errcode(ERRCODE_DUPLICATE_OBJECT),
 				 errmsg("role \"%s\" already exists", newname)));
 
-	if (strcmp(newname, "public") == 0 ||
-		strcmp(newname, "none") == 0)
-		ereport(ERROR,
-				(errcode(ERRCODE_RESERVED_NAME),
-				 errmsg("role name \"%s\" is reserved",
-						newname)));
-
 	/*
 	 * createrole is enough privilege unless you want to mess with a superuser
 	 */