tests: Don't wait for frame callbacks when a surface is on no outputs

The event-test moves a client off of all the outputs to check for an
output leave event, but our move_client() code waits on a frame callback
to continue.

The fact that weston currently generates this frame callback is not
something we should enforce in a test, as it could (should) change in
the future.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>