GNUmakefile: move editor settings to .editorconfig

Remove inline vim/emacs editor configuration,
add makefile to editorconfig instead.

.editorconfig

@@ -42,3 +42,12 @@ insert_final_newline = true
 indent_style = space
 indent_size = 3
 max_line_length = 120
+
+# Makefile
+[{Makefile,GNUmakefile}]
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = tab
+indent_size = 4
+max_line_length = 120

GNUmakefile

@@ -1,6 +1,3 @@
-# -*- mode: gnumakefile; tab-width: 4; indent-tabs-mode: t; -*-
-# vim: tabstop=4
-#
 # ##### BEGIN GPL LICENSE BLOCK #####
 #
 #  This program is free software; you can redistribute it and/or