chore: clarify wait for idle params

juju/model.py

@@ -2867,7 +2867,6 @@ async def _get_source_api(self, url):
     # - pretty common, const value or parametric
     # - rarely used with 0 units, after explicit .scale(scale=0)
     # - there's a test for 0 units, implying that all apps are gone
-    # - may be used with N apps, N units with a mapping {app_name: unit_count}
     async def wait_for_idle(self,
         apps: Optional[List[str]] = None,
         raise_on_error: bool = True,
@@ -2944,7 +2943,6 @@ async def wait_for_idle(self,
         units_ready: Set[str] = set()  # The units that are in the desired state
         last_log_time: List[Optional[datetime]] = [None]
 
-        # FIXME seems inconsistent wrt. use in integration tests
         if wait_for_exact_units is not None:
             assert isinstance(wait_for_exact_units, int) and wait_for_exact_units >= 0, \
                 'Invalid value for wait_for_exact_units : %s' % wait_for_exact_units