'git replace' parses the revision arguments when it creates replacements
(so that a sha1 can be abbreviated, e.g.) but not when deleting
replacements.
Make it parse the argument to 'replace -d' in the same way.
Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Jeff King <peff@peff.net>