Remove brew dependencies (#172)

diff --git a/.cirrus.yml b/.cirrus.yml
index 9928498..b708d7f 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -44,10 +44,6 @@
       BUILD_SHARDING: "--shardIndex 0 --shardCount 2"
       BUILD_SHARDING: "--shardIndex 1 --shardCount 2"
   setup_script:
-    - brew update
-    - brew install libimobiledevice
-    - brew install ideviceinstaller
-    - brew install ios-deploy
     - pod repo update
     - git clone https://github.com/flutter/flutter.git
     - git fetch origin master