`git fetch --tags` seems to interact badly with `mirror=fetch`, resulting in
the regular branches not being fetched, so drop the unnecessary `--tags`. This
fixes this unit test failure: `bb.fetch2.FetchError: Fetcher failure: Unable
to resolve 'master' in upstream git repository in git ls-remote output for
/tmp/tmp4ag_mgmn/gitsource`
[YOCTO #11698]
(Bitbake rev: 2d0203fae08c5ff8dc3e9afaa9a819abc4a1af6f)
Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>