[GHC] #8894: Clean up `Coercible` plumbing

[GHC]

#8894: Clean up `Coercible` plumbing
-------------------------------------+-------------------------------------
              Reporter:  nomeata     |            Owner:  nomeata
                  Type:  task        |           Status:  closed
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            Resolution:  wontfix     |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:  #8904
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D300   |
-------------------------------------+-------------------------------------
Changes (by nomeata):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 SPJ says  at https://phabricator.haskell.org/D300#15193 that we probably
 won’t need this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8894#comment:14>
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