Remove no_adjacent_strings_in_list from enabled lint rules.

[srawlins]

no_adjacent_strings_in_list conflicts with another rule, prefer_adjacent_string_concatenation. I suggest removing the former.

See dart-lang/linter#4076

prefer_adjacent_string_concatenation is a style-oriented rule, but it is in the package:lints recommended set. So... it is recommended.

no_adjacent_strings_in_list is an error-preventing lint rule, but it's usefulness is waning, as the new style of the Dart formatter will always split adjacent strings into new lines.

We are marking these two lint rules as incompatible. If the fix in this PR is not desired, there are two other options:

• Remove prefer_adjacent_string_concatenation from the enabled lint rules.
• Insert an # ignore: comment in the top-level analysis options file, and an # ignore: included_file_warning comment in any files that include the top-level one.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[stuartmorgan]

We should comment this out with an explanation, as with most other lints we don't use use (see the rest of the file), rather than removing it.

It's unfortunate that we're having to turn off a useful warning before we get the formatter change that would make the mistake the warning would catch obvious though.

[srawlins]

I'll convert to draft for a bit.