www-client/netsurf: drop netsurf eclass

www-client/netsurf: drop netsurf eclass

The netsurf project has tons of little single-purpose libraries that
aren't used in any other project. That causes us to create many packages
*and* maintain an eclass for a program that isn't the most popular (it
had been completely broken for 3 months until a few weeks ago).

In this commit, I take the worst offenders and bundle them directly in
netsurf's ebuild. The long term goal is to eventually get rid of the
netsurf eclass by reducing the number of packaged netsurf libs (and thus
make the copy-paste of ebuild boilerplate less painful).

Other changes:

* Drop multilib. I really don't see the point of it and it adds needless
  complexity.
* Drop fb.modes. This is related to directfb, which isn't supported in
  Gentoo any more.
* Drop "linux" and "able" frontends. They aren't listed in libnsfb's
  supported frontends.
* Allow more than one fb frontend to be selected.
* Don't set NETSURF_FB_FRONTEND. It has no effect.

Closes: https://bugs.gentoo.org/669714
Signed-off-by: Virgil Dupras <vdupras@gentoo.org>
Package-Manager: Portage-2.3.51, Repoman-2.3.11