Remove option to immediately commit pref changes on import

[XiangRongLin]

What is it?

• Codebase improvement (dev facing)

Description of the changes in your PR

Follow up to #6495. See commit messages for detailed descriptions

• Remove option to immediately commit pref changes on import
• Resolve sonar issues in ContentSettingsFragment
• Remove variable ContentSettingsFragment.lastImportExportDataUri

APK testing

On the website the APK can be found by going to the "Checks" tab below the title and then on "artifacts" on the right.

I tested it manually on API 28 emulator

1. by exporting the settings
2. moving the exported file somewhere else
3. trying to import and verify that the file explorer opens the old correct path
4. navigate to the moved file and import
5. verify that another export now opens to the new file location.

Due diligence

• I read the contribution guidelines.

[Stypox]

For some reasons when the app is restarted I get the "The language will change once the app is restarted." toast, even though the language is correctly changed and updated throughout the app (I tried setting to a random language and then importing a database with "Use system language" language). Other than that I tested and it works well ;-)

[opusforlife2]

@Stypox I see the same thing on the 0.21.6 RC and all the current debug APKs, so it can't be due to this PR. See #3312 (comment).

[Stypox]

You are right @opusforlife2. Then I'm approving this :-)