Update Gaia API documents for #24823a14069fee495b34d693d79bcf02a1da8764
    Revert "Bug 944718 - [Cost Control] Broken access to usage widget from utility tray"

This reverts commit 31bbe151e0d92da77a86a3ae5edb6ca2643968e1.

This is the second time this patch has been backed out.
https://bugzilla.mozilla.org/show_bug.cgi?id=944718