init: handle -c conflicts with gitc-init

We keep getting requests for init to support -c.  This conflicts with
gitc-init which allocates -c for its own use.  Lets make this dynamic
so we keep it with "init" but omit it for "gitc-init".

Bug: https://crbug.com/gerrit/10200
Change-Id: Ibf69c2bbeff638e28e63cb08926fea0c622258db
(cherry picked from commit 66098f70)
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/253392


Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>