Error index links should be hidden

[hsyl20]

GHC now displays error links. doctest shouldn't display them:

Example:

/home/hsyl20/projects/haskus/packages/haskus-binary/src/lib/Haskus/Binary/Bits.hs:96: failure in expression `getPowerOfFour (10 :: Word)'
expected: Nothing
 but got: <interactive>:603:1: error: [\ESC]8;;https://errors.haskell.org/messages/GHC-88464\ESC\\GHC-88464\ESC]8;;\ESC\\]
          ^
              Variable not in scope: getPowerOfFour :: Word -> t

Notice the error: [\ESC]8;;https://errors.haskell.org/messages/GHC-88464\ESC\\GHC-88464\ESC]8;;\ESC\\]

While it should better be: error: [GHC-88464]