[GHC] #15045: Remove broken top-level shell.nix

[GHC]

#15045: Remove broken top-level shell.nix
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           Reporter:  mpickering     |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.2.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):  Phab:D4599     |         Wiki Page:
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 The shell.nix in the root directory is quite broken. The one at
 hadrian/shell.nix should be used. I'm not even sure how that shell.nix
 ended up there. I don't remember adding it.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15045>
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