Remove backup service

[nalcalag]

Task/Issue URL: https://app.asana.com/0/0/1206314482566716/f

Description

This PR contains the removal of the Google backup service implementation to persist ATB

Steps to test this PR

• Go to develop
• Add a file under the Android directory called test_d2d.sh
• Copy and paste in this new file the code from https://app.asana.com/0/0/1206310480197408/f
• Install from develop
• Run ./test_cloud_backup.sh com.duckduckgo.mobile.android.debug to perform a backup
• Check in File Explorer, you have com.duckduckgo.app.statistics.backup file with the atb key in it
• Install from this branch
• Refresh File Explorer
• Check com.duckduckgo.app.statistics.backup has been cleared

No UI changes

[nalcalag]

In this stack: 🔥 Streamline infrastructure by removing backup service

• develop
  • Remove backup service #4061 👈

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[nalcalag]

I kept this class because the new approach will be also added here so we can assign ru variant before initialisation.
I thought it was a good place to also add the preferences removal for the moment.

[marcosholgado]

LGTM