all: Remove third argument to MP_REGISTER_MODULE.

It's no longer needed because this macro is now processed after
preprocessing the source code via cpp (in the qstr extraction stage), which
means unused MP_REGISTER_MODULE's are filtered out by the preprocessor.

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

py/modstruct.c

@@ -266,6 +266,6 @@ const mp_obj_module_t mp_module_ustruct = {
     .globals = (mp_obj_dict_t *)&mp_module_struct_globals,
 };
 
-MP_REGISTER_MODULE(MP_QSTR_ustruct, mp_module_ustruct, MICROPY_PY_STRUCT);
+MP_REGISTER_MODULE(MP_QSTR_ustruct, mp_module_ustruct);
 
 #endif