Revert "Parallel jenkins (pull request #397)"
Revert "Parallel jenkins (pull request #397)"

This reverts pull request #397.

> Perform tests in parallel on jenkins.
> 
> Jenkins Blue Ocean 2.0 is now released, enabling the parallel syntax to declarative pipelines. Now HOOMD tests can run in parallel on the Jenkins platform providing faster time to test completion.
joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue