[code-reflection] Integrated: Remove redundant type variables

[Paul Sandoz]

Remove redundant type variables from the ONNX operator API.

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Commit messages:
 - Remove redundant type variables.

Changes: https://git.openjdk.org/babylon/pull/315/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=315&range=00
  Stats: 117 lines in 2 files changed: 24 ins; 19 del; 74 mod
  Patch: https://git.openjdk.org/babylon/pull/315.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/315/head:pull/315

PR: https://git.openjdk.org/babylon/pull/315