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/objnone.c

@@ -47,8 +47,7 @@ MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_NoneType,
     MP_QSTR_NoneType,
     MP_TYPE_FLAG_NONE,
-    print, none_print,
-    unary_op, mp_generic_unary_op
+    print, none_print
     );
 
 #if !MICROPY_OBJ_IMMEDIATE_OBJS