Don't modify params dict on parametrized tests

Multiple backend tests (e.g. openssl and commoncrypto) receive the same params dicts, but we were modifying them using pop. This PR modifies the lambdas of our tests to allow us to pass the params through without modifying them.

The other (simpler) approach was simply to copy the dict, but our memory consumption is already through the roof for the full test suite so the less copies resident in memory the better...