[SB] Remove old SignalCallback from CastTile.java.

The old SIGNAL_CALLBACK_DEPRECATION flag has been launched for years, so
this CL removes the old code in CastTile.java related to that flag.

Bug: 291315866
Flag: EXEMPT removing launched code
Test: manual: Verify Cast tile is disabled if not connected to wifi,
enabled if connected to wifi
Test: atest CastTileTest

Change-Id: I6da0e90bdbc4ae5ada461637ba4fe84e83c37d88