Cache call removal future to enable canceling it when we retry

When retrying emergency calls over a new CS, enable telecom to
cancel a pending removal from the old CS because
CreateConnectionProcessor will handle the removal internally.

Bug: 341157874
Flag: com.android.server.telecom.flags.cancel_removal_on_emergency_redial
Test: manual E2E testing
Change-Id: I6fc96a7ffbadffb31e26c4f391ba6fe9e46d3dac