py/obj: Remove mp_generic_unary_op().

Since converting to variable sized slots in mp_obj_type_t, we can now
reduce the code size a bit by removing mp_generic_unary_op() and the
corresponding slots where it is used. Instead we just implement the
generic `__hash__` operation in the runtime.

Signed-off-by: David Lechner <david@pybricks.com>

py/objsingleton.c

@@ -45,8 +45,7 @@ STATIC void singleton_print(const mp_print_t *print, mp_obj_t self_in, mp_print_
 
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_singleton, MP_QSTR_, MP_TYPE_FLAG_NONE,
-    print, singleton_print,
-    unary_op, mp_generic_unary_op
+    print, singleton_print
     );
 
 const mp_obj_singleton_t mp_const_ellipsis_obj = {{&mp_type_singleton}, MP_QSTR_Ellipsis};