SysUI A11y: Fix keyguard time utterance

The fancy colon on keyguard is causing issues for TalkBack.
Fixed by replacing it with a regular colon in accessibility infos.

Change-Id: Id4802a8dc422f2abb523dbbf887291d5983fd4ee
Fixes: 34949557
Test: runtest -x /frameworks/base/packages/SystemUI/tests/src/com/android/keyguard/KeyguardClockAccessibilityDelegateTest.java
Test-Manual: Enable talkback, make sure that lockscreen time is read out correctly