RFR: webrev: do not fetch remote branches

[Erik Helin]

Hi all,

please review this patch that makes webrev use the branches under `remote/`
(e.g. `origin/`) to when calculating the closest remote branch. There is no need
to fetch the remote branches.

Testing:
- Manual testing of `git webrev`

Thanks,
Erik

-------------

Commit messages:
 - webrev: do not fetch remote branches

Changes: https://git.openjdk.java.net/skara/pull/560/files
 Webrev: https://webrevs.openjdk.java.net/skara/560/webrev.00
  Stats: 18 lines in 1 file changed: 14 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/skara/pull/560.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/560/head:pull/560

PR: https://git.openjdk.java.net/skara/pull/560