[TASK] Drop .travis.yml

Travis CI for core has been flaky for a while - processes
tend to die or are queued forever. The only thing travis
still executed for us is updating sonar cloud data.
This service has been introduced some years ago but did
never find significant usage and has never been configured.

The patch drops travis along with sonar-cloud. If anyone
wants to pick up work with sonar again, it could be added
as github action again.

Change-Id: I2929bfb1f72d1a6af273692b4f632d90280bf074
Resolves: #93084
Releases: master, 10.4, 9.5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/67144


Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>