Remove use of `NIX_GHC_LIBDIR` in ghcide

[jneira]

• The use of the env vars has been removed from hie-bios, it seems it is not needed anymore (in other case it should be added again)

haskell-language-server/ghcide/session-loader/Development/IDE/Session/VersionCheck.hs

Line 17 in 17fce67

ghcVersionChecker = $$(makeGhcVersionChecker (fromMaybe GHC.Paths.libdir <$> lookupEnv "NIX_GHC_LIBDIR"))

//cc @pepeiborra