This reverts commit b419957e.

* [Refactor] use getCustomOp instead of direct registry access

* [Refactor] move HLSCustomOp base to own file

* [Refactor] register all HLSCustomOps in new style

* [Refactor] use correct domain for custom ops acc. to new style

* [Deps] update finn-base to get new-style customop domains

* [Refactor] more domain fixes

* [Test] fix ipstitch expected io values in rtlsim

* [Deps] update finn-base and brevitas

* [Docs] link to CustomOp reorg PR

1000 labels with low folding creates very large, long-running test cases

turns out there was a problem with signed values after all
failing testcases with k=5 produce the indices of positive values correctly, but negative ones don't seem to be compared correctly (always producing index 0?)