ports: Use default VFS config for import_stat and builtin_open.

For ports with MICROPY_VFS and MICROPY_PY_IO enabled their configuration
can now be simplified to use the defaults for mp_import_stat and
mp_builtin_open.

This commit makes no functional change, except for the following minor
points:
- the built-in "open" is removed from the minimal port (it previously did
  nothing)
- the duplicate built-in "input" is removed from the esp32 port
- qemu-arm now delegates to VFS import/open

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

ports/zephyr/main.c

@@ -195,22 +195,16 @@ mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
 }
 #endif
 
+#if !MICROPY_VFS
 mp_import_stat_t mp_import_stat(const char *path) {
-    #if MICROPY_VFS
-    return mp_vfs_import_stat(path);
-    #else
     return MP_IMPORT_STAT_NO_EXIST;
-    #endif
 }
 
 mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
-    #if MICROPY_VFS
-    return mp_vfs_open(n_args, args, kwargs);
-    #else
     return mp_const_none;
-    #endif
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
+#endif
 
 NORETURN void nlr_jump_fail(void *val) {
     while (1) {