ci: drop mention of BREW_INSTALL_PACKAGES variable

The last user of this variable went away in 4a6e4b9 (CI: remove
Travis CI support, 2021-11-23), so it's doing nothing except making it
more confusing to find out which packages _are_ installed.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

ci/install-dependencies.sh

@@ -34,8 +34,6 @@ macos-*)
 	export HOMEBREW_NO_AUTO_UPDATE=1 HOMEBREW_NO_INSTALL_CLEANUP=1
 	# Uncomment this if you want to run perf tests:
 	# brew install gnu-time
-	test -z "$BREW_INSTALL_PACKAGES" ||
-	brew install $BREW_INSTALL_PACKAGES
 	brew link --force gettext
 
 	mkdir -p "$P4_PATH"