Uninstall curl before running debian-bootstrap

debian-bootstrap attempts to install cabal-install-1.16, which can either work with curl, wget, or fetch, in that order of preference. Unfortunately the hackage URLs have changed since 1.16, and with the arguments which were used in cabal-install's bootstrap script in 1.16, curl doesn't follow 301 redirects.

The simplest solution is to uninstall curl, so that wget is used instead.