refactor: remove dead M4MODPATH code. * m4/m4private.h (USER_MODULE_PATH_ENV): Remove. * m4/module.c: Correct doc-comment header details. (m4__module_init): Remove PKGLIBEXECDIR and M4MODPATH handling. Move configmake.h include from here... * m4/path.c: ...to here. (m4__include_init): Append PKGLIBDIR to search path. Signed-off-by: Gary V. Vaughan <gary@gnu.org>