Some of these tests were originally written as part of a custom `run-make`
test, so at that time they weren't able to use the normal compiletest header
directive parser.
Now that they're properly integrated, there's no need for them to use
`compile-flags` to specify the edition, since they can use `edition` instead.
Some of these tests use non-standard formatting that we can simulate by
strategically adding `//` line comments.
One contains `where` clauses that would be split across multiple lines, which
we can keep on one line by moving the bounds to the generic type instead.
