remove the dep on package:ansicolor

[devoncarew]

• remove the dependency on package:ansicolor

This is work towards generally reducing the number of deps that devtools has. Note that the package:ansicolor had been a regular dep of devtools_app, but it looks like it was only ever referenced from tests.

Please add a note to packages/devtools_app/release_notes/NEXT_RELEASE_NOTES.md if your change requires release notes. Otherwise, add the 'release-notes-not-required' label to the PR.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or there is a reason for not adding tests.

If you need help, consider asking for help on Discord.