Apply suggestions from code review

Co-authored-by: Sean Quah <[email protected]>

synapse/handlers/device.py

@@ -456,7 +456,7 @@ async def check_device_registered(
         raise errors.StoreError(500, "Couldn't generate a device ID.")
 
     async def _prune_too_many_devices(self, user_id: str) -> None:
-        """Delete any stale devices this user may have."""
+        """Delete any excess old devices this user may have."""
         device_ids = await self.store.check_too_many_devices_for_user(user_id)
         if not device_ids:
             return

synapse/storage/databases/main/devices.py

@@ -1541,7 +1541,7 @@ async def check_too_many_devices_for_user(self, user_id: str) -> Collection[str]
         )
 
         # We let users have up to ten devices without pruning.
-        if num_devices < 10:
+        if num_devices <= 10:
             return ()
 
         # We prune everything older than N days.