emacs-module.c simplification and tuneup

emacs-module.c simplification and tuneup

* src/emacs-module.c (CHECK_USER_PTR): New function.
(module_get_user_ptr, module_set_user_ptr)
(module_get_user_finalizer, module_set_user_finalizer): Use it.
(module_make_global_ref, module_copy_string_contents)
(module_make_string, module_vec_set, module_vec_get): Omit
unnecessary runtime tests.  For example, vector sizes are always
fixnums, so we don’t need to test that they are in fixnum range.