mac: Remove buildbot-only toolchain creds code.

buildbot was turned down a while ago, so this should no longer be needed.

Bug: 986488
Change-Id: Ie7496a5647814f6d526bfe212a4637873c90a37b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212318
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771286}

build/mac_toolchain.py

@@ -107,13 +107,6 @@ def InstallXcodeBinaries():
       'cipd', 'ensure', '-root', binaries_root, '-ensure-file', '-'
   ]
 
-  # Buildbot slaves need to use explicit credentials. LUCI bots should NOT set
-  # this variable. This is temporary code used to make official Xcode bots
-  # happy. https://crbug.com/986488
-  creds = os.environ.get('MAC_TOOLCHAIN_CREDS')
-  if creds:
-    args.extend(['--service-account-json', creds])
-
   p = subprocess.Popen(
       args, stdin=subprocess.PIPE, stdout=subprocess.PIPE,
       stderr=subprocess.PIPE)