don't store mDatabase in SQLiteCursor as it is already in SQLiteQuery

SQLiteCursor has two members: mQuery, mDatabase
but mQuery already has mDatabase.
there is no need for SQLiteCursor.mDatabase.
and everytime SQLiteQuery.mDatabase is to be used, try to use a pooled database
connection handle, if possible.
Change-Id: I42b2376d714a1a4091c843e245a45b882bb7fee6