ElevenUtils: remove custom RejectedExecutionHandler

This is an artifact from a time long gone.
AsyncTask implements a default RejectedExecutionHandler, which
prints a warning about exceeding queue size and initializes
a backup executor, which will run the task.

Running it on a backup executor is actually better than trying
to reclaim space from the executor and trying to rerun the task
on it.

Change-Id: I981bc2598ff240e72fbe4ae43e79d3a4534fa242
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>