Remove unnecessary configChangeFlags

The field is only non-zero when relaunching activity, i.e.
sending a ActivityRelaunchItem. So the flag is unnecessary
to be a field of ActivityRecord and other lifecycle items
don't need an always-zero field.

Bug: 163976519
Test: atest ObjectPoolTests ClientTransactionItemTest
Change-Id: I6741807ff7b6b3fee2acfcb711ea3bba8c9f71ed