Removed 'fastClear' capability.

No need for 'fastClear' anymore. Current modes are:
1. fullReset: Reinstall the app.
2. noReset: Don't reinstall, keep app data.
3. fastReset (!fullReset && !noReset): Don't reinstall the app, but clear the app data (pm clear).
Merge pull request #2117 from paymand/remove_fast_clear

Removed 'fastClear' capability.