Removed unused AspNet.Net35 Net35Backport

This backport class became obsolete after fixing the PreBodyTagFilter with pull request #456 

Now to keep the codebase free from to much dead code, I would like to remove it, but before merging this into master, I want to make sure that everybody agrees on this, because I can imagine a couple of reasons not to do it, and so the question is more how likely they will be:

- The backport will be used somewhere in the future again (can't tell for sure)
- Somebody uses this class outside of the Glimpse code base inside their own application code (unlikely!?)

At least this pull request will make sure the dead code is "marked".

Any thoughts on this one?