[TASK] Drop composer API token from travis build

Since Github removed the API limit for non authenticated requests
to get an archive link, we can safely remove the token without
loosing the benefit of faster composer builds.

Resolves: #76889
Releases: 7.6, master
Change-Id: I6cffcc3bf17915ac3d4d99dcaafa9be3406ff5bc
Reviewed-on: https://review.typo3.org/48750


Reviewed-by: Steffen Müller <typo3@t3node.com>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>