Disable unit tests. They require ocamlopt, which isn't available on all Debian architectures, and Gaëtan Gilbert says that "they don't test much yet" anyway.
Also disable .vio tests, as they run afoul of https://github.com/coq/coq/issues/9141.
Remove heavyweight tests Remove tests that use too much RAM or time to run on a buildd. (The MIPS buildd is frequently the culprit, as MIPS lacks an OCaml native compiler.)
A number of tests (mostly for coq_makefile) assume that Coq is installed when the test runs. This isn't true in an sbuild environment, though, so disable those tests.
