Move filterMobileSubscriptionInSameGroup into KeyguardUpdateMonitor.

This avoids race condition that, KeyguardUpdateMonitor refreshes active
sub list however CarrierTextController filtered it based on stale active
data subId.

By move filterMobileSubscriptionInSameGroup into KeyguardUpdateMonitor,
it becomes the single source of truth about which carrier name should be
shown.

Bug: 138456731
Bug: 151600673
Test: manual and unittest
Change-Id: Ida3a90c5408b056cad7a79fbba84fe880ce1e5be
Merged-In: Ida3a90c5408b056cad7a79fbba84fe880ce1e5be
(cherry picked from commit 5c63b51d)