Remove reform files from repo

[jdebacker]

Given past discussions (such as in Issue #2445), I think the maintainers of this project have decided that the best thing to do is to move the example reform JSON file out of this repository. As a result, the PSL/examples repository has been created.

Since PSL/examples have been set up, it may be a good time to move the reform files from this repository.

To do this one should:

1. Delete files from Tax-Calculator/taxcalc/reforms
2. Update units tests that point to reform file URLs to point to them in the PLS/examples repo.
3. Consider creating a GH Action that tests reform files in PSL/examples on a new Tax-Calculation version release (see PSL/examples Issue #10)

[jdebacker]

As I drafted PR #11 in the examples repo, it occurred to me that we might want to make a distinction between different types of "reform" files.

For example, it might be helpful to archive all changes to law in the Tax-Calculator repository. See Issue #2610 for a discussion of why it is useful to be able to move backwards in time with tax law to represent baseline policy at different points in time.

Thus, one could think about keeping all reform files that reflect enacted changes to tax law in the Tax-Calculator repository (perhaps renaming the "reforms" folder to something else like "policy_changes") and moving all proposed (but not enacted) policy reforms to the examples repository.

Thoughts?

cc @MattHJensen

[jdebacker]

Per discussions in the Tax-Calculator developer meeting, it was decided that JSON files of enacted law changes will remain in the Tax-Calculator repo and proposed (but not enacted) policies will be moved to the PSL examples repo.