Discontinue usage of Danger

[php-coder]

The idea is nice but

1. it takes time for maintenance
2. the project has no committers other than myself, so I don't see a reason to keep using Danger. Also, as part of migration to GitHub Actions (Migrate from Travis CI to GitHub Actions #1154) I have to invest time for its migration and I don't see it worth it

Related issues:

• Migrate to DangerJS #1210
• Danger: handle errors from Jest #1564 (0pdd)
• Danger: handle Babel errors from frontend-maven-plugin #1071 (0pdd)
• Danger: highlight a failed spock test #761 (0pdd)
• Automate code review process with Danger (maximum requirements) #537
• [WIP] PR for testing danger #533

[php-coder]

DANGER_GITHUB_API_TOKEN has been deleted from Travis CI as well.