Refactor a couple reduces into a couple somes

I think it's a little simpler this way.
#1269: Skip tests differently when using :test-selectors

The old method skipped tests by adding a hook to
clojure.test/test-var, the problem being that :each fixtures
associated with the test have already run at that point, which is
unideal.

This change skips test by removing their :test metadata before running
the tests at all, which causes clojure.test to not see it as a test.

We use ns-interns to enumerate the vars, the same way clojure.test
does.
Minor cleanup from PR feedback
Merge pull request #1271 from fredericksgary/issue-1269

Issue 1269