Delete mController when eventHub device is going away

When an event hub device is going away, the controller associated with
it should be deleted.

Before this CL, mController would remain, and its use would result in an
illegal memory access, because it was storing a reference to a deleted
context.

Bug: 245770596
Test: atest inputflinger_tests:InputDeviceTest#DumpDoesNotCrash
Change-Id: I298f43172472f74fa4d5d8e0b7f52bd5c13d14f7