feat: add delete-files flag

[incendial]

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix
[ ] New rule
[ ] Changes an existing rule
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[X] Other, please explain: add a new flag to automatically delete unused files

[github-actions]

Dart Code Metrics analyze report of dart_code_metrics. ✅

Summary

• Scanned folders: bin, example, lib, test

• Total scanned files: 357

• Total lines of source code: 6368

• Total classes: 240

• Average Cyclomatic Number per line of code: 0.35 / 1

• Average Source Lines of Code per method: 6

• Total tech debt: 1034.0 hours

• Found issues: 6 ⚠

[codecov]

Codecov Report

Merging #632 (8cf2b18) into master (09038f6) will decrease coverage by 0.11%.
The diff coverage is 69.69%.

❗ Current head 8cf2b18 differs from pull request most recent head 8562d56. Consider uploading reports for the commit 8562d56 to get more accurate results

@@            Coverage Diff             @@
##           master     #632      +/-   ##
==========================================
- Coverage   86.15%   86.04%   -0.12%     
==========================================
  Files         234      235       +1     
  Lines        5013     5029      +16     
==========================================
+ Hits         4319     4327       +8     
- Misses        694      702       +8     

Impacted Files	Coverage Δ
lib/src/analyzers/lint_analyzer/lint_analyzer.dart	93.75% <0.00%> (ø)
..._list/code_climate/lint_code_climate_reporter.dart	100.00% <ø> (ø)
.../reporters_list/console/lint_console_reporter.dart	100.00% <ø> (ø)
...rs/reporters_list/github/lint_github_reporter.dart	100.00% <ø> (ø)
...orters/reporters_list/html/lint_html_reporter.dart	0.31% <ø> (ø)
...orters/reporters_list/json/lint_json_reporter.dart	100.00% <ø> (ø)
...reporters_list/json/unused_l10n_json_reporter.dart	100.00% <ø> (ø)
...ib/src/reporters/models/code_climate_reporter.dart	100.00% <ø> (ø)
lib/src/reporters/models/console_reporter.dart	100.00% <ø> (ø)
lib/src/reporters/models/github_reporter.dart	100.00% <ø> (ø)
... and 13 more

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[dkrutskikh]

@incendial if we remove all unused files, why we in alarm state? I think this is good or info state, our repo not contains unused files.

[incendial]

Fixed

[dkrutskikh]

@incendial why this is async function? I see only sync methods.

[incendial]

Fixed

[github-actions]

Dart Code Metrics unused files report of dart_code_metrics. ✅

Summary

• Scanned package folders: bin, example, lib
• No unused files found! ✅