Drop obnam-sha1 from results

obnam show-ref isn't working, and I can't be bothered to deal
with this. I'll be satisfied with just git describe output.

1 files changed, 0 insertions, 2 deletions

diff --git a/obnam-benchmark b/obnam-benchmark
index 6d3ccd16..32aff739 100755
--- a/obnam-benchmark
+++ b/obnam-benchmark
@@ -344,11 +344,9 @@ class ObnamBenchmarkRunner(cliapp.Application):
 
     def get_version_info_dict(self):
         treeish = self.settings['obnam-treeish']
-        sha1 = cliapp.runcmd(['git', 'show-ref', treeish]).split()[0]
         describe = cliapp.runcmd(['git', 'describe', treeish]).strip()
         return {
             'obnam-treeish': treeish,
-            'obnam-sha1': sha1,
             'obnam-version': describe,
             'larch-version': larch.__version__,
             }