Revert "Specify a branch to pull from explicitly in RefreshManifestCheckout."
Revert "Specify a branch to pull from explicitly in RefreshManifestCheckout."

This reverts commit b144650ea3da23e8beae1657b11d5e09ee469b2f

Suspected of breaking canaries.

BUG=chromium-os:27547
TEST=None

Change-Id: I30aff9d005c4b5a2d5873d47f51145ba5e4429d1
Reviewed-on: https://gerrit.chromium.org/gerrit/17638
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

zhang0137/chromite,chadversary/chromiumos.chromite,coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,coreos/chromite