Fix macOS CI (#2345)

old-commit-hash: 72a996a885

tools/mac_setup.sh

@@ -1,13 +1,7 @@
 #!/bin/bash -e
 
-# Install brew if required.
+echo "Updating Homebrew"
-if [[ $(command -v brew) == "" ]]; then
+brew update
-    echo "Installing Hombrew"
-    /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
-else
-    echo "Updating Homebrew"
-    brew update
-fi
 
 brew install capnp \
              czmq \