Remove the last of my notes. I don't think these really need to be in

the release notes despite their awesomeness. If we had a thorough
discussion of the performance of Clang in 2.9 vs. 3.0, the first would
be more relevant, but we don't. The serialization stuff hopefully isn't
terribly visible to end users.

Objections to these omissions are of course welcome. =]

llvm-svn: 145336