Remove fs files from rts install-includes.

Summary:
They don't really need to be installed and will fix Hadrian installs.
Skipping review because change is trivial.

THis should be safe, but running it through CI to be sure.

Test Plan: ./validate

Reviewers: bgamari, erikd, simonmar

Subscribers: thomie, carter

Differential Revision: https://phabricator.haskell.org/D4591

rts/rts.cabal.in

@@ -129,8 +129,6 @@ library
                       rts/Timer.h
                       rts/Types.h
                       rts/Utils.h
-                      rts/fs.h
-                      rts/fs_rts.h
                       rts/prof/CCS.h
                       rts/prof/LDV.h
                       rts/storage/Block.h