Update test generators to use tests.toml files

PR #821 added `tests.toml` files for all exercises. We should update our test generator to only generate tests for the test cases that are in the `tests.toml` files and where the test is included (meaning its UUID is assigned `true` as its value).

The test generator should also remove the line at the top of generated test files that contains the versioning information (which is no longer present).

Depends on #822 being done first.