[TRAVIS] Remove DOCKER_SECRETS from travis file
[TRAVIS] Remove DOCKER_SECRETS from travis file

Since the fork check is based on TRAVIS_SECRET_ENV_VARS and we no longer
use docker containers for testing, we don't need these variables
anymore.

CiscoCloud/microservices-infrastructure,CiscoCloud/mantl,KaGeN101/mantl,CiscoCloud/microservices-infrastructure,CiscoCloud/mantl,mantl/mantl,mantl/mantl,KaGeN101/mantl