bitbake: fetch2: Change git fetcher not to destroy old references

It looks like we're about to see a lot of changes in branch names in repos. If
we have the prune option here, those old names are lost, the changes propagate
to our source mirrors and our old releases break.

We have the force option so any replaced references should be replaced, its only
orphaned branches which will now be preserved.

I believe this behaviour will cause us fewer problems given the changes that
look likely to happen.

(Bitbake rev: 1df4fb1c9bf2fde0b274374bff1235c4b1f7ac79)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/git.py

@@ -359,7 +359,7 @@ class Git(FetchMethod):
               runfetchcmd("%s remote rm origin" % ud.basecmd, d, workdir=ud.clonedir)
 
             runfetchcmd("%s remote add --mirror=fetch origin %s" % (ud.basecmd, repourl), d, workdir=ud.clonedir)
-            fetch_cmd = "LANG=C %s fetch -f --prune --progress %s refs/*:refs/*" % (ud.basecmd, repourl)
+            fetch_cmd = "LANG=C %s fetch -f --progress %s refs/*:refs/*" % (ud.basecmd, repourl)
             if ud.proto.lower() != 'file':
                 bb.fetch2.check_network_access(d, fetch_cmd, ud.url)
             progresshandler = GitProgressHandler(d)