Bug#942585: FTBFS with ghc-8.6.5 on ppc64el

[Ilias Tsitsimpis]

Source: gtk2hs-buildtools
Version: 0.13.4.0-2
Severity: serious
Tags: ftbfs
Justification: fails to build from source (but built successfully in the past)
Forwarded: https://gitlab.haskell.org/ghc/ghc/issues/17203

This package FTBFS with ghc-8.6.5 on ppc64el. Let's remove it from
testing for now, to allow the rest of the Haskell packages to migrate.

-- 
Ilias