Remove user configuration for spellchecking
In Bug 772622, we introduced the spell check (for annotations).
Somehow, we got into discuss to add an option to enable and disable the spellchecking.
It has been bothering me for a while, and I agree the first @carlosgc comment that we should just use it if it enabled in compilation time.
We have not made any release yet with it, so we still can remove it from the menu and from gsettings; and there will be no regression.