qemu/mpconfigport: Enable VFS reader, loading .mpy files and io.IOBase.

This allows importing from the VFS, and enables the following 7 additional
tests: builtin_execfile, io_iobase, json_dump_iobase, import_mpy_invalid,
import_mpy_native, import_mpy_native_gc, vfs_userfs.

Signed-off-by: Damien George <damien@micropython.org>

ports/qemu/main.c

@@ -71,10 +71,6 @@ void gc_collect(void) {
     gc_collect_end();
 }
 
-mp_lexer_t *mp_lexer_new_from_file(qstr filename) {
-    mp_raise_OSError(MP_ENOENT);
-}
-
 void nlr_jump_fail(void *val) {
     mp_printf(&mp_plat_print, "uncaught NLR\n");
     exit(1);