Revert "Enforce that a PendingIntent has an explicit mutability ..."

Revert "PendingIntentTest: Add tests to check enforced mutabilit..."

Revert submission 13048968-pi-enforce-mutability-flag

Reason for revert: Lots of regressions since merging this, reverting to address those.
Reverted Changes:
If49be6141:Enforce that a PendingIntent has an explicit mutab...
I885d1b558:PendingIntentTest: Add tests to check enforced mut...

Change-Id: I371cef3b423c23736b520ca5c29ee4ff9c51bb33