Martin von Zweigbergk <martinvonz@google.com> [Mon, 04 Nov 2019 14:58:58 -0800] rev 4918
obslog: don't overwrite {rev} keyword from changeset context
Now that we have the whole changeset in the formatter context, there's
no need to explicitly add {rev}.
We should also deprecate the {shortdescription} keyword since it's no
longer needed, but I don't know how to do that.