Fix double speaking "disconnected" when leader #18710
Closes #18692
Summary of the issue:
When connected as the controlling computer, disconnecting causes NVDA to speak "Disconnected" twice.
Description of user facing changes:
NVDA speaks "Disconnected" once.
Description of developer facing changes:
None
Description of development approach:
Removed superfluous ui.message from _remoteClient.client.RemoteClient.onDisconnectedAsLeader.
