Remove pylint from Travis-CI

Since we now rely on Scrutinizer-CI for linting features we can safely
remove our home brewed solution of running pylint and uploading the
results to S3. The S3 upload has been disabled for some time now, this
just cleans up the .travis.yml configuration file.
Merge pull request #595 from plajjan/travis-ci/remove-pylint

Remove pylint from Travis-CI configuration