Remove some recently-added pg_dump test cases.

Remove some recently-added pg_dump test cases.

Commit d2d35479796c3510e249d6fc72adbd5df918efbf included a pretty
extensive set of test cases, and some of them don't work on all
of our Windows machines. This happens because IPC::Run expands
its arguments as shell globs on a few machines, but doesn't on most
of the buildfarm. It might be good to fix that problem systematically
somehow, but in the meantime, there are enough test cases for this
commit that it seems OK to just remove the ones that are failing.

Discussion: http://postgr.es/m/3a190754-b2b0-d02b-dcfd-4ec1610ffbcb@dunslane.net
Discussion: http://postgr.es/m/CA+TgmoYRGUcFBy6VgN0+Pn4f6Wv=2H0HZLuPHqSy6VC8Ba7vdg@mail.gmail.com