Add firefox/os/devices
Revert "Add firefox/os/devices"

This reverts commit 498145102e5c25faf6ff8ebd0249a7a0c1dc0898.
Add firefox/os/devices, without removing anything
NIT: array indent
Adding es-MX to os/index + os/devices
Adding es-MX for os/faq

(adding as well since the file is already translated)