Revert "Merge pull request #19765 from wilsonpage/1008187"

This reverts commit 392123a9c53fd9a6ccbb1c81908c3176c0647222, reversing
changes made to 54d6512f516564c23e4363ca328b2a453605617b.
Bug 1018393 - Disable intermittent failing test, failing test, test_a11y_keyboard_key_names.py test_a11y_keyboard_key_names.TestA11yKeyboardKeyNames.test_a11y_keyboard_key_names
Bug 1013929 - Use the languagechange event instead of a mozSettings observer. r=stas
Merge pull request #19835 from zbraniecki/1013929-languagechange

Bug 1013929 - Use the languagechange event instead of a mozSettings observer. r=stas
Bug 1017314: Load tutorial config in a loadConfig method.

* New unit tests, fixes existing FTU tests with setup.js and misc path/dependency issues
* Start tutorial preload in ftu UIManager.init
* Use l10nKey as property name in config
* Refactor Tutorial to loadConfig/ensureConfig and update tests accordingly
* Use shared mock_navigator_moz_setttings, delete the ftu one as its no longer used (c.f. bug 1017893)
* Remove unused data-maxstep attributes.
Bug 990035 - Modify phone-sized tutorial to show vertical-scroll, notifications & sheets video
Placeholder video assets
play() videos when we enter that step