Revert "Bug 987418 - Update copy in fxa system app r=ferjm"

This reverts commit 01f9a841050c5f66f511f34804e298b3ec1dd30d.
Merge pull request #18384 from 6a68/revert-bug-987418

Revert "Bug 987418 - Update copy in fxa system app r=ferjm"