Delete redundant cloudfoundry-cli

The recipe is redundant--Cloud Foundry is maintaining its own homebrew
tap (see https://github.com/cloudfoundry/cli#downloads) which has the
most up-to-date version of the CLI. Rather than maintaining up-to-date
versions of the CLI in two separate homebrew taps (i.e. Cask and
Pivotal), it's simpler to use one: the canonical one (i.e. Pivotal) and
remove it from the other (Cask).