wipe all url.* bits prior to syncing.
wipe all url.* bits prior to syncing.

Do this since certain hosts have url.$HOST.insteadof in use, in addition
to the previous .pushinsteadof.

Having things like this mangling the repo when the repo is reused leads
to random breakage when the manifest repoints at a different url prefix.

BUG=chromium-os:24413
TEST=n/a, old hosts

Change-Id: I67d900273b033b715eaa3f432b12aa49e8df2806
Reviewed-on: https://gerrit.chromium.org/gerrit/13552
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Reviewed-by: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>
Commit-Ready: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>

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