Revert "travis: Add a workaround for a bug regarding libtool installed via Homebrew"

This reverts commit 1806ba0890 as the
workaround is not required anymore and now actually fails because
pre-installed tools have a dependency on libtool.

scripts/test.sh

@@ -292,8 +292,6 @@ if test "$1" = "deps"; then
 		;;
 	osx)
 		brew update && \
-		# workaround for issue #6352
-		brew uninstall --force libtool && brew install libtool && \
 		brew install $DEPS
 		;;
 	freebsd)