Remove scrape missing previews option

[hjiangsu]

Pull Request Description

This PR removes the remaining logic for scrape missing previews option mentioned in #1720. I've also added a migration step to remove existing instances of setting_general_scrape_missing_previews in SharedPreferences.

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?

[micahmo]

LGTM!

Is there also a package we were using for this feature that could possibly be removed now?

[hjiangsu]

Is there also a package we were using for this feature that could possibly be removed now?

There's the link_preview_generator package which was originally used for scraping but was later replaced by our own getLinkInfo function. From what I can tell, link_preview_generator is still used in two places:

• The bottom sheet when long-pressing on a link
• The create post page when generating a suggested title for a URL

While this is out of scope for this PR, we could fully remove link_preview_generator by updating these use-cases to use getLinkInfo instead!