[code-reflection] RFR: Drop ClosureOp and ClosureOpCall

[Maurizio Cimadamore]

As we have dropped support for quoted structured lambdas, the corresponding code model `ClosureOp` is no longer used and can be removed as well. That also drags `ClosureOpCall`, as that op is only used to call closure ops. And the related `TestClosureOps` test.

I didn't find any occurence of the removed class in examples/HAT.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/babylon/pull/668/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=668&range=00
  Stats: 315 lines in 4 files changed: 0 ins; 315 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/668.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/668/head:pull/668

PR: https://git.openjdk.org/babylon/pull/668