Remove mac_toolchain hook as XCode is now installed via recipe

TBR=machenbach@chromium.org

Bug: chromium:863607
Change-Id: I1352bc236e7e236d70130db7fcc4333821fdec70
Reviewed-on: https://chromium-review.googlesource.com/1238924
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56178}

DEPS

@@ -339,13 +339,6 @@ hooks = [
     'condition': 'checkout_win',
     'action': ['python', 'v8/build/vs_toolchain.py', 'update'],
   },
-  {
-    # Update the Mac toolchain if necessary.
-    'name': 'mac_toolchain',
-    'pattern': '.',
-    'condition': 'checkout_mac',
-    'action': ['python', 'v8/build/mac_toolchain.py'],
-  },
   # Pull binutils for linux, enabled debug fission for faster linking /
   # debugging when used with clang on Ubuntu Precise.
   # https://code.google.com/p/chromium/issues/detail?id=352046