Bug 1791084 - Add "AC-" to treeherder platform names

This reverts commit 2db89572.

This reverts commit c2b26663.

This reverts commit e3363bbd.

In addition to the requirements bump itself, this means:
- bump decision-mobile docker image
- rename job-defaults to task-defaults, jobs to tasks, job-template to task-template
- stop setting parameters that are now handled by taskgraph upstream

Android-components releases are now scheduled from shipit, so we don't
need to trigger any extra tasks when a release is published.

This has become unnecessary for 2 reasons:
- this code hasn't worked since switching to python3, due to differences in how
  unicode strings are represented
- "artifact-map" is excepted in upstream taskgraph since
  https://github.com/taskcluster/taskgraph/commit/842359ecd7c0bdde862238930864ebc105d4e289

Bug 1783690 - part 8: Let `android-gradle-dependencies` read `.buildconfig.yml` from the right folder