Remove unused GHC compat code (#3412)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: fendor

ghcide/ghcide.cabal

@@ -229,10 +229,6 @@ library
     if flag(ghc-patched-unboxed-bytecode)
       cpp-options: -DGHC_PATCHED_UNBOXED_BYTECODE
 
-    if impl(ghc < 8.10)
-      exposed-modules:
-        Development.IDE.GHC.Compat.CPP
-
     if impl(ghc >= 9)
         ghc-options: -Wunused-packages