Don't use custom prelude for latest ghc.
This is a better approach to making 'stack ghci' and 'cabal repl'
work. Instead of using NoImplicitPrelude, we only use the custom
prelude for older ghc versions. The custom prelude presents a
uniform API that matches the current base version's prelude.
So, when developing (presumably with latest ghc), we don't
use a custom prelude at all and hence have no trouble with ghci.
The custom prelude no longer exports (<>): we now want to
match the base 4.8 prelude behavior.
c1e474f005