Remove Nuxeo Android Connector documentation

In the context of NXMOB-229 it was decided to deprecate the Nuxeo Android Connector because:

• It has not been maintained for a long time and we don't plan to.
• We want to push people to use:
  • The Nuxeo Java client to build an Android application.
  • The Mobile app and maybe in the future the React Native framework we will get out of it to build custom apps for both platforms.

We moved https://github.com/nuxeo/nuxeo-android/ to https://github.com/nuxeo-archives

Now we need to remove/deprecate the related documentation: https://doc.nuxeo.com/nxdoc/nuxeo-android-connector/ and its subpages.
Once this is done let's reference the removal commit from https://github.com/nuxeo/doc.nuxeo.com-content in the README of the nuxeo-android archived repository.

We might want to write something about the reason why it was deprecated and the way to go and handle redirections.
+ update https://doc.nuxeo.com/nxdoc/android-client/