Some cases had to stay behind, either because they required complex case
configuration that we don't support in independent files yet, or because
they have associated comments which we don't want to lose track of.
To make sure I didn't drop any tests in the process, I logged all
obj/test/exe test cases from a run of "zig build test" and compared
before/after this change.
All of the test cases match, with two exceptions:
- "use of comptime-known undefined function value" was deleted, since
it was a duplicate
- "slice sentinel mismatch" was renamed to "vector index out of
bounds", since it was incorrectly named
