patch 8.2.4136: Vim9: the "autoload" argument of ":vim9script" is not useful

Problem:    Vim9: the "autoload" argument of ":vim9script" is not useful.
Solution:   Remove the argument. (closes #9555)
diff --git a/src/errors.h b/src/errors.h
index e576f81..0d11416 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3208,8 +3208,7 @@
 	INIT(= N_("E1261: Cannot import .vim without using \"as\""));
 EXTERN char e_cannot_import_same_script_twice_str[]
 	INIT(= N_("E1262: Cannot import the same script twice: %s"));
-EXTERN char e_using_autoload_in_script_not_under_autoload_directory[]
-	INIT(= N_("E1263: Using autoload in a script not under an autoload directory"));
+// E1263 unused
 EXTERN char e_autoload_import_cannot_use_absolute_or_relative_path[]
 	INIT(= N_("E1264: Autoload import cannot use absolute or relative path: %s"));
 EXTERN char e_cannot_use_partial_here[]