git_command: drop custom version helper

Since ParseGitVersion can call `git --version` automatically, we don't
need this duplicate version() helper anymore.  The only other user is
the `repo version` code, so convert that to version_tuple().full.

Bug: https://crbug.com/gerrit/11144
Change-Id: I9d77822fc39f4ba28884d9183359169cabf5f17d
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/231055
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>
diff --git a/subcmds/version.py b/subcmds/version.py
index 8b48bcf..9fb694d 100644
--- a/subcmds/version.py
+++ b/subcmds/version.py
@@ -41,5 +41,5 @@
       print('repo launcher version %s' % Version.wrapper_version)
       print('       (from %s)' % Version.wrapper_path)
 
-    print(git.version().strip())
+    print('git %s' % git.version_tuple().full)
     print('Python %s' % sys.version)