Don't escape edited summary text

This key (contentFormat) was recently changed.
I'm changing it back because there are other places (revision.content.format)
where this is still just 'format' (and that revision.content is returned by
edit-summary API and fed to the template, which assumed 'contentFormat' instead
of 'format')

If there was a particular reason to change it to contentFormat, it can be
changed back, just make sure to also change revision.content.format (and every
place that may affect)

Change-Id: Id97ce78dc41b150d37dac419ec0aabc42b5930d7