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/javascript/mpconfigport.h

@@ -175,10 +175,6 @@ typedef int mp_int_t; // must be pointer size
 typedef unsigned mp_uint_t; // must be pointer size
 typedef long mp_off_t;
 
-// extra built in names to add to the global namespace
-#define MICROPY_PORT_BUILTINS \
-    { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },
-
 // We need to provide a declaration/definition of alloca()
 #include <alloca.h>