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