Remove useless code.

The only use of mDeleteCount is to implement delete
acceleration. It's reset at each non-delete code point, and
is guarded by a timer.
Plus, ultimately we want to remove this completely :
acceleration should be implemented by actually deleting
stuff faster, not by deleting several code points at a time.

Change-Id: Ia3144860b3aa2499034f2a2a7c81f32087af9598