SystemUI: Remove visibility check in setting QSCarrier color

This fixes a corner case where the signal icon color is incorrect:
Have dual sim -> switch to dark theme -> turn off one sim -> switch
to light theme -> turn the other sim back on. QS carrier signal
is colored white instead of black.

Ensure that the signal icon color is always up to date, by removing
visibility check, to avoid this issue.

Fixes: 816b8ddf ("Follow light/dark theme in SplitShade Header")
Change-Id: I092c06053fc4bc8d9ca51d1d31128da27ef6a823