Remove Travis integration testing

This reverts these commits:

* 930a27a47e633a312f62037ce9dba6247a1fdfd5.
* 922dbcb6d79287f4813ba3ccf4c05ad409051b05.
* 8b565cf25819862f7d059e50a44237456615db12.
* 50fc5d07d82d883a3fef13d5f61267a996cd2c4a.