bug#34131: File Variable doc: Remove the quotes on "variable"

[Eli Zaretskii]

> From: 積丹尼 Dan Jacobson
>       <jidanni@jidanni.org>
> Date: Sat, 19 Jan 2019 08:45:10 +0800
> 
> In (info "(emacs) Safe File Variables")
> 
>    File-local variables can be dangerous; when you visit someone else’s
>    file, there’s no telling what its local variables list could do to your
>    Emacs.  Improper values of the ‘eval’ “variable”, and other variables
> 
>                                             ^        ^ please remove the
>                                             quotes on “variable”.

It's in quotes because it isn't really a variable, it's a function
call in disguise.