Bug#911024: src:haskell-monadplus: unmaintained

[Clint Adams]

On Sun, Oct 14, 2018 at 05:01:16PM -0700, Sean Whitton wrote:
> Just to note in the bug that the reason haskell-monadplus was packaged
> was for agda, which still build-depends on it.  So if we don't think
> monadplus is worth the maintenance burden, neither is agda; we should
> get rid of that too.  (I don't have an opinion on this as I am not
> maintaining either.)

agda 2.5.4.1 no longer build-depends on it so this particular problem
 will be resolved whenever there are binary builds of agda/unstable.