Drop default-extensions:CPP in hpc-bin.cabal

The utils/hpc/*.hs code doesn't use any CPP statements anyway, so this
extensions was redundantly enabled to begin with.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

utils/hpc/hpc-bin.cabal

@@ -46,5 +46,4 @@ Executable hpc
                        containers >= 0.1 && < 0.6,
                        array      >= 0.1 && < 0.6
     Build-Depends: hpc
-    Default-Extensions: CPP