Move keys removal to background handler.

After 600 app uninstalls, the delay as compared to immedate call:
50%	0ms
75%	1ms
90%	1.2ms
95%	3.1ms
99%	12.04ms
99.9%	62.216ms

Bug: 220083428
Test: presubmit
Change-Id: I73d18283a49beb7724a8f86a5767c28970ba8170