audit SVN accesses

one of things that came out of the SVN retirement discussion is that we don't exactly know how to tell who has access to what. we hope that access controls are correct and tight, but that institutional knowledge somewhat bitrotten over the years, so we can't easily tell.

the task is to figure out exactly which set of users has access to which files.

this is in the context that the SVN service will be eventually retired, but we have hit a roadblock in the corpsvn retirement (legacy/trac#32025 (moved)) where there are concerns about where to move the files to. so while we resolve those concerns, we will keep hosting corpsvn for a little longer and that means cleaning up the accesses.