Splitting fish into multiple packages was what the downstream Debian
packaging does, but it provides minimal benefit to end-users installing
from the fish repositories and in some cases made it harder. The only
benefit was a slightly reduced size on disk for download repositories.
Closes#7845.
Reverts 45ae726d4f and solves #3053
through a Conflict with fish-common.
CMake 3.5 (shipped in Ubuntu Xenial) doesn't generate the test target
with appropriate dependencies. Build them in dh_auto_build; it's too
hard to convince any of the other steps to do it.
See #7851.
The autoreconf step requires a newer version of automake than is
available on older versions of Debian and Ubuntu; avoid the autoreconf
step on these platforms for now.