Documentation/git-reflog: convert to use synopsis type

Documentation/git-reflog: convert to use synopsis type

With 974cdca345c (doc: introduce a synopsis typesetting, 2024-09-24) we
have introduced a new synopsis type that simplifies the rules for
typesetting a command's synopsis. Convert the git-reflog(1)
documentation to use it.

While at it, convert the list of options to use backticks. This is done
to appease an upcoming new linter that mandates the use of backticks
when using the synopsis type.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>