Since the only way we can get to clear_index() is with
indexfile having previously been assigned
indexfile = git.repo(b'bupindex')
since opt.clear and opt.indexfile are explicitly mutually
exclusive, there's no point in calling git.repo() again,
it has no effect.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net> Reviewed-by: Rob Browning <rlb@defaultvalue.org> Tested-by: Rob Browning <rlb@defaultvalue.org>