Remove --detach flag from "git checkout"
Remove --detach flag from "git checkout"

It fails on older versions of git.

R=rmistry@google.com

Review URL: https://codereview.chromium.org/24240011

git-svn-id: 32fc27f4dcfb6c0385cd9719852b95fe6680452d@11400 2bbb7eff-a529-9590-31e7-b0007b416f81

Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot