Remove Travis

[frantz45]

Travis isn't used anymore, anything related to it should be removed (from all projects).
It would be cleaner and more secure because we gave some accesses to Travis.
Moreover there was a security alert on this topic: https://github.blog/2022-04-15-security-alert-stolen-oauth-user-tokens/.

[c8y3]

For each project, we need to remove :

• travis webhooks when they exist
• travis github app (should be done at the organization level)

[VincentD06]

No Travis webhook or github app at project level.
No Travis webhook or github app at the organization level (check with an administrator).