Don't keep shadowed variables in ghci, both renamer and type checker
In #14052 (closed), we reverted D2447, then #11547 (closed) exists in HEAD again. In ticket:14052#comment:151549 and ticket:14052#comment:140478, we decide that shadowed variables shouldn't be keep at all. This ticket is created to track the idea.
$ inplace/bin/ghc-stage2 --interactive GHCi, version 8.5.20180403: http://www.haskell.org/ghc/ :? for help Prelude> 1 1 Prelude> 1 1 Prelude> _ <interactive>:1:1: error: GHC internal error: ‘Ghci1.it’ is not in scope during type > checking, but it passed the renamer tcl_env of environment: 
(giving "1" twice is needed to reproduce the error)
NB: input "1" twice to create shadowed context is necessary to reproduce this bug.