rustdoc: Remove .woff font files
Copying `@jsha's` great comment:
> Right now we ship 1.5MB of woff files in the rustdoc binary, and 1MB of woff2 files, for a total of 2.5MB.
>
> Per:
>
> https://caniuse.com/woff
> https://caniuse.com/woff2
>
> The only listed browser that supports woff and not woff2 is IE, which is not supported per https://github.com/rust-lang/rfcs/blob/master/text/1985-tiered-browser-support.md.
>
> I propose we stop shipping woff files and save 1.5MB from the rustdoc binary (and from each doc build).
r? `@jsha`