[bot] Remove obsolete l10n strings and ftl files

### Remove obsolete strings
Search the code base for [strings marked `obsolete`](https://github.com/search?q=repo%3Amozilla%2Fbedrock+obsolete+language%3AFluent&type=code&l=Fluent) that are more than 2 months old.
If you find strings that have no date, either find the date by looking at git history
or add an expiry date and leave it to be removed in 2 months.
- [ ] Remove old obsolete strings
### Remove obsolete ftl files
Compare the files in /l10n/en-US/ to the /en/ folder in the www-l10n repo and remove
files from www-l10n that no longer exist in bedrock.
If you have both repos installed and up to date you can run this command:
`diff -r www-l10n/en bedrock/l10n/en | grep ".ftl"`
- [ ] Remove files
- [ ] Remove references in www-l10n/configs/pontoon.toml

Compare bedrock/l10n/en with www-l10n/en, using the provided diff command if both repositories are available and current. Search for Fluent strings marked obsolete, check dates through git history where needed, and inspect www-l10n/configs/pontoon.toml for references. Done means removing eligible strings, obsolete files, and their configuration references.

Written by the indexing model from the issue text.