Remove last transition info after it is logged

Otherwise if the activity calls Activity#reportFullyDrawn every
time after it is created, the metrics will be reported again
with unexpected values if it is relaunched, e.g. rotation change.

Bug: 123355661
Test: No "Fully drawn" log by activity relaunched
Change-Id: I16bd816c8f0af8c28c2b2ac38994d9daa9c0ba96