Fix for not being able to return to InCallUI after accepting call via BT

No longer require that the activity was previously started for
bringToForeground to work. That check seemed to be unnecessary and was
causing problems in the case when the UI hadn't been shown previously
(e.g. accepting a call via BT).

Tested with the following scenarios:
1) Accepting an incoming call HUN via finger
2) Returning to in-call screen via dialer after accepting HUN via BT
3) Returning to in-call screen via lock screen after accepting HUN via BT
4) Returning to in-call screen via notification after accepting HUn via BT
5) Accepting a full screen call via BT
6) Receiving call waiting
7) Adding a new call
8) Conference calls

Bug: 17654200
Change-Id: I4886c9a611a71fd04eeb154960293f6b1494b4b2