This reverts commit d48784e6 for causing nightly cron failures.

* Use nightly Fenix variant.

* Run the tests in PR.

* Update visual-metrics scripts to include the similarity metrics.

* Use python3.5 in visual-metrics docker.

* Install wget in the docker.

* Use python3.6 hashes instead of python3.5.

* Undo run-visual-metrics.py python changes.

* Upgrade python setuptools version to 46.1.3.

* Add setuptools to transitive dependency list.

* Undo PR test changes.

* Remove setuptools install line and use requirements.txt instead.

* Undo PR test changes.

* Fix geckodriver artifact suffix.

* Test a browsertime task.

* Revert browsertime test.

* Add visual-metrics docker type.

* Add required browsertime toolchain fetches.

* Add browsertime tests for technical and visual metrics.

* Run browsertime tests in a cron task.

* Run visual metrics on all browsertime tests.

* Use spaces instead of tabs, and resolve visual-metric nits.

* Enable browsertime on pull request for testing.

* Restrict PR tests to amazon on browsertime.

* First attempt using multi_dep.

* Add a primary dependency to browsertime.

* Try by not popping.

* Debug prints.

* Make one grouping per browsertime task.

* Try without the multi_dep transform.

* Delete dependent-tasks in visual-metrics transformer.

* Update setuptools installed and copy run-on-tasks-for.

* Use get when getting run-on-tasks-for.

* Add new pinned requirements.

* Try it.

* Set run-on-tasks-for properly.

* Remove print statement.

* Remove single_dep loader, and print statements.

* Remove run-on-tasks-for testing setting.

* Restart testing, and set user to root in visual-metrics Docker.

* Remove testing settings.

* Remove fetch-content from Docker.

* Change attributes grouping method.

* Run all tests as a check.

* Undo testing changes, and fix a bad test name.