Remove dependency on mod_depends

[lrowe]

I have an old fork of mod_transform to support running xslt on html for Diazo theming. Now that mod_transform is on Github, it'd be great to see if it might be possible to merge my changes. I'll post each group of changes as an issue as some work will be required to rebase on to current master.

I've found that mod_depends emits broken caching headers for dynamic or proxied content. This patch removes it completely: lrowe/mod_transform@90ce85e. If that's undesirable perhaps there needs to be a setting to disable it.