Modify overlay settings of cache clearing dialog

Previously, CacheClearingActivity needlessly used
SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS and TYPE_APPLICATION_OVERLAY.

These flags are not needed for our purposes and in addition they make us
request extra permissions that we don't need.

This CL removes those flags.

Test: manual
Bug: 155290762
Change-Id: Ie606a7ba0afad1da26115a2bb48a1852787ecd36
2 files changed