Remove notification settings screens

[lorenzoPrimi]

Some changes to do in the setting screen and preferences, they are all interconnected but they serve different purposes:

• Remove local notification setting. This is just an overcomplication for the user and will be removed forever, both in the screen and preferences array.

• Remove notification preference screen in fdroid bundle, remove it at all. So in that flavor there will be no notification menu item.

• Comment push notification setting item in the full flavor. As notifications are not used in the moment the entry of this setting screen will be just commented in the master branch (and uncommented in the countly branch)

[lorenzoPrimi]

ooni/probe-ios#346 and ooni/probe-android#310 have been opened.
When they will be approved I'd need to

• Merge master into the countly and automated_testing branch
• Re-add notification preference in the countlybranch
• Fix the local notification in the automated_testing branch