doc fix: remove the text about the non-existing clock specification

shared-bindings/time/__init__.c

@@ -215,7 +215,7 @@ STATIC mp_obj_t time_time(void) {
 MP_DEFINE_CONST_FUN_OBJ_0(time_time_obj, time_time);
 
 //| def monotonic_ns() -> int:
-//|     """Return the time of the specified clock clk_id in nanoseconds.
+//|     """Return the time of the monotonic clock, cannot go backward, in nanoseconds.
 //|
 //|     :return: the current time
 //|     :rtype: int"""