remove jsonschema benchmark

[braingram]

As asdf no longer depends on jsonschema the benchmark that tests jsonschema will fail (as it's not installed).

This PR removes the jsonschema benchmark.

This should fix: https://github.com/spacetelescope/bench/issues/72

Checklist:

• [ ] pre-commit checks ran successfully
• [ ] tests ran successfully
• [ ] for a public change, a changelog entry was added
• [ ] for a public change, documentation was updated
• [ ] for any new features, unit tests were added

[zacharyburnett]

wow, how did you see that so fast?