cellular: Remove unused BlackHoleContext

BUG=chromium:404003
TEST=Verify BlackHoleContext not used via code search

Change-Id: I0f1438cbeaf1b228aebb70cd83fd4db58f07cd75
Reviewed-on: https://chromium-review.googlesource.com/213367
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Thieu Le <thieule@chromium.org>
1 file changed