Use final GHC build from bootstrap

Let GHC be pulled in as a normal dependency of xmonad and other Haskell
packages.

Containerfile

@@ -15,8 +15,6 @@ RUN puppet agent --test --certname ci --environment main --tags nest::base::dist
 # it also needs to be persisted in the image.
 ENV LANG=en_US.UTF-8
 
-RUN ACCEPT_KEYWORDS='* ~*' emerge -v1 -j1 dev-libs/libffi dev-lang/ghc
-
 # Switch to desired profile and make the base system consistent with it,
 # breaking out of a possible circular dependency between mesa and libva.
 RUN eselect profile set "nest:${PROFILE}"

haskell.conf

-[haskell]
-location = /var/db/repos/haskell
-sync-type = git
-sync-uri = https://gitlab.james.tl/nest/gentoo/haskell.git
-sync-depth = 1
-auto-sync = yes