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/objtype.c

@@ -1112,7 +1112,6 @@ MP_DEFINE_CONST_OBJ_TYPE(
     make_new, type_make_new,
     print, type_print,
     call, type_call,
-    unary_op, mp_generic_unary_op,
     attr, type_attr
     );