This removes the final traces of Travis and Appveyor from the Flutter tree.
I've updated the documentation and fixed a couple of places where scripts look for Travis, and eliminated the dart tools runningOnTravis function (which was unused anyhow).
There are places in the flutter script that used to look for the environment variable TRAVIS. We actually do want to continue to detect that we're running on Travis there, since in the plugins repo we still use Travis (for the moment). In any case, it's OK, because the CI environment variable is set on all of the CI bots (Cirrus, Travis, and Appveyor).
FastLane doesn't have a setup_cirrus equivalent to setup_travis, but it actually doesn't matter there either, since it doesn't do Travis-specific things, and it also looks for the CI environment variable.
* Revert "Roll engine to 6473f1b106485cb0b4ea569af383173daeef8895 (#16032)"
This reverts commit 844ced010a.
* Revert "Let travis test archiving per commit too (#16004)"
This reverts commit df5905f382.
* iOS works
* Works on Android
* Take in commit number in iOS also. Get rid of image upload for Android. It's just a waste of bandwidth
* Tweak to fix on Travis
* first round fastlane working on Android
* clean up and start ios
* Partial iOS
* Got a fastfile that works on iOS
* Finalize Android push instructions
* Finalize instructions for iOS
* Extra cleanup and optipng
* Disable readme autogen and add a default readme
