haskell: aeson-schema missing test suite

For some reason the .tar.gz on hackage is missing most of the files for
the test suite.  I've opened an issue on
it (https://github.com/timjb/aeson-schema/issues/9), but it's not yet
been acted on.  In the meantime, simply disabling the test suite seems
most sensible.

@peti, could you merge this?