Remove dead code in modules/webdatabase/, part 2.

This CL removes the following unused functions/variables:
- DatabaseAuthorizer::setReadOnly
- DatabaseContext::hasOpenDatabases
- DatabaseManager::hasOpenDatabases
- SQLResultError
- SQLResultSchema
- SQLiteStatement::getColumnDouble
- SQLiteStatement::returnTextResults

BUG=none
TEST=none
R=morrita@chromium.org

Review URL: https://codereview.chromium.org/130963005

git-svn-id: svn://svn.chromium.org/blink/trunk@165379 bbb929c8-8fbe-4397-9dbb-9b2b20218538