[websql] remove Database::markAsDeletedAndClose and related code

It's dead code, we never call it

BUG=none
R=michaeln@chromium.org

Review URL: https://codereview.chromium.org/85443002

git-svn-id: svn://svn.chromium.org/blink/trunk@162681 bbb929c8-8fbe-4397-9dbb-9b2b20218538