patch 8.2.3977: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/userfunc.c b/src/userfunc.c
index eb2ee1c..dac7df8 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3268,7 +3268,7 @@
 		break;
 	case FCERR_NOTMETHOD:
 		emsg_funcname(
-			N_("E276: Cannot use function as a method: %s"), name);
+			N_(e_cannot_use_function_as_method_str), name);
 		break;
 	case FCERR_DELETED:
 		emsg_funcname(e_function_was_deleted_str, name);