[Ongoing Call] Remove #onEntryCleanUp override.

With ag/15924211 submitted, #onEntryRemoved should be correctly called for both pending and active entries, so we no longer need to care about #onEntryCleanUp.

See https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/base/+/15924211/comments/d96f2662_c42f3b88.

This effectively reverts commit cd755525.

Test: Tested with test app referenced in ag/15909288 and confirmed that b/199600334 still does not occur.
Bug: 199600334
Change-Id: I31a0c805f05ca9b00be68fe3e30b2d249c16a7ab