[GHC] #10913: deprecate and then remove -fwarn-hi-shadowing

[GHC]

#10913: deprecate and then remove -fwarn-hi-shadowing
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        Reporter:  osa1              |                Owner:  ChrisU
            Type:  task              |               Status:  new
        Priority:  lowest            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
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Comment (by osa1):

 We should either implement or remove it, leaving it there unimplemented is
 the worst case, because it has an entry in user manual and man page etc.
 and users may expect it to work while it silently does nothing.

 Since nobody complained in 9 years, I say let's remove it.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10913#comment:4>
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