[infra] Use Xcode from CIPD.

Change-Id: I0ae2869accd22c57e06460cb56f5d7cc116d9782
Reviewed-on: https://skia-review.googlesource.com/146120
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
3 files changed