close() on anything other than database shouldn't acquire db lock.

bug:2683001
implmentation details:
 1.close() on any sql statement is should simply queued up for finalization
    to be performed later. caller doesn't acquire database lock.
 2. the only effect of NOT close immediately is non-release of some memory.
 3. all such queued-up-finalizations are performed whenever there is
    another execute() of some sql statement on that database from ANY
    thread in the process.
 4. database close() automatically releases all unfinalized statements
    before closing the database.

Change-Id: If4c9c7fde6b8945a41abc6c8b992aa8c69854512