Revert 195613 "Reenable test_isolate_mode=check by default on OSX."

Revert 195613 "Reenable test_isolate_mode=check by default on OSX."

Speculating this is the cause of these OS X release builder hangs:

http://build.chromium.org/p/chromium.mac/builders/Mac%20Builder/builds/11074/steps/compile/logs/stdio
http://build.chromium.org/p/chromium.chrome/builders/Google%20Chrome%20Mac/builds/12424/steps/compile/logs/stdio

Relevant compile output:

=== BUILD AGGREGATE TARGET base_unittests_run OF PROJECT base WITH CONFIGURATION Release ===
Check dependencies

PhaseScriptExecution "Rule \"isolate\"" ../xcodebuild/base.build/Release/base_unittests_run.build/Script-5816EF986C49795B2FAB6114.sh
cd /Volumes/data/b/build/slave/cr-mac-rel/build/src/base
/bin/sh -c /Volumes/data/b/build/slave/cr-mac-rel/build/src/base/../xcodebuild/base.build/Release/base_unittests_run.build/Script-5816EF986C49795B2FAB6114.sh
python ../tools/swarm_client/isolate.py check --outdir "/Volumes/data/b/build/slave/cr-mac-rel/build/src/base/../xcodebuild/Release/ " --variable PRODUCT_DIR "/Volumes/data/b/build/slave/cr-mac-rel/build/src/base/../xcodebuild/Release " --variable "OS=mac" --result "/Volumes/data/b/build/slave/cr-mac-rel/build/src/base/../xcodebuild/Release/base_unittests.isolated" --isolate "base_unittests.isolate" --ignore_broken_items

command timed out: 1200 seconds without output, attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=4205.819860


> Reenable test_isolate_mode=check by default on OSX.
> 
> This is not necessary to default to noop anymore. Defaulting to check was
> disabled on OSX because a problem during archival with symlink path case. This
> was fixed inside swarm_client.
> 
> R=csharp@chromium.org
> BUG=98637
> 
> Review URL: https://chromiumcodereview.appspot.com/14404011

TBR=maruel@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=195664

[Mike Wittman, 2013-04-23 00:45:04]

Committed patchset #1 manually as r195664.