Pretty: delete really old changelog
Pretty: delete really old changelog

This changelog is very incomplete, and basically useless. I'm removing
it, because it made it harder to compare this copy of `Pretty.hs` with
the copy in `libraries/pretty` (from which a similar changelog was
deleted some time ago).

(cherry picked from commit 372dbc4e78abfb6b5d72c0fea27a1c858c5cd797)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc