Drop support for FreeBSD

.gitlab/before_script/freebsd/install_deps.sh

-#!/bin/sh
-
-set -eux
-
-# pkg install --force --yes --no-repo-update curl gcc gmp gmake ncurses perl5 libffi libiconv
-
-. "$( cd "$(dirname "$0")" ; pwd -P )/../../ghcup_env"
-
-mkdir -p "${TMPDIR}"
-
-curl -sSfL https://downloads.haskell.org/~ghcup/x86_64-portbld-freebsd-ghcup > ./ghcup-bin
-chmod +x ghcup-bin
-
-./ghcup-bin install ${GHC_VERSION}
-./ghcup-bin install-cabal ${CABAL_VERSION}
-./ghcup-bin set ${GHC_VERSION}
-
-exit 0