Delete bugreport file on bugreport cancel

Note: bugreport Cancel is not the same as bugreport onError. Files are not
deleted onError, as it still has some information before the bugreport
crashed/stopped. Bugreport Cancel is triggered by the user, hence clean
up all the files.

Bug: 146994281
Test: Cancel interactive bugreport from UI, deletes the current
bugreport files

Change-Id: I2606e491cbaa20eaa60980e98af56a194bae2280