Revert "ci: Add subject_type to createReviewComment()"

This reverts commit 211cd6e9a3.

They document it here:
https://octokit.github.io/rest.js/v22/#pulls-create-review-comment
but apparently that's out of date and this doesn't work anymore.

.github/workflows/claude-review.yml

@@ -486,7 +486,6 @@ jobs:
                   commit_id: c.commit,
                   path: c.path,
                   line: c.line,
-                  subject_type: "line",
                   body: `Claude: **${c.severity}**: ${c.body}`,
                 });
                 posted++;