Revert "Replace hermetic Xcode installation with CIPD-based flow."

This reverts commit 116dd7c3.

Reason for revert: broke https://ci.chromium.org/buildbot/chromium.webkit/WebKit%20Mac%20Builder/240835

Original change's description:
> Replace hermetic Xcode installation with CIPD-based flow.
> 
> The 'API' to the scripts remains the same, only the delivery mechanism changes.
> 
> BUG=797051
> R=​erikchen@chromium.org, justincohen@chromium.org
> 
> Change-Id: I8ee5486b107061f9fb6e64354463ac51de53d4cc
> Reviewed-on: https://chromium-review.googlesource.com/887819
> Reviewed-by: John Budorick <jbudorick@chromium.org>
> Reviewed-by: Erik Chen <erikchen@chromium.org>
> Commit-Queue: Sergey Berezin <sergeyberezin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#553871}

TBR=erikchen@chromium.org,justincohen@chromium.org,sergeyberezin@chromium.org,jbudorick@chromium.org

Change-Id: Icdd25e048a8ed6de19b7a98e41a438c1c7c6ed2f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 797051
Reviewed-on: https://chromium-review.googlesource.com/1029630Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Commit-Queue: Sergey Berezin <sergeyberezin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553876}

build/mac/should_use_hermetic_xcode.py

@@ -30,7 +30,7 @@ def _IsCorpMachine():
 def main():
   allow_corp = sys.argv[1] == 'mac' and _IsCorpMachine()
   if os.environ.get('FORCE_MAC_TOOLCHAIN') or allow_corp:
-    if not mac_toolchain.PlatformMeetsHermeticXcodeRequirements():
+    if not mac_toolchain.PlatformMeetsHermeticXcodeRequirements(sys.argv[1]):
       return "2"
     return "1"
   else: