Deprecate DatabaseUtils.InsertHelper.

This class does not offer any advantages over SQLiteStatement
and just makes code more complex and error-prone.

Documented that the class is not thread-safe.

Removed a potential deadlock in insert() and replace() caused
by the insertInternal() method being synchronized in the case
where the class was being used concurrently (woe to you!).

Thread A would start a transaction.
Thread B would call insertInternal() and acquire the object monitor,
but block because it could not obtain the db connection because
thread A is holding onto it.
Thread A would call insertInternal() and block because Thread B
was holding the object monitor.
Deadlock.

Changed this code to use a transaction instead of a lock,
which provides the necessary mutual exclusion guarantee without
the potential for a deadlock.  Even so, the class really isn't
thread safe.

Bug: 6625094
Change-Id: I51d9a15567a6f2bad6f25e550b48f8f6ffcab2a7