validateChildKeys in packages/react/src/jsx/ReactJSXElement.js had a signature
of validateChildKeys(node, parentType), but #34174 ("Remove unused arguments from
ReactElement") dropped the second argument, changing the signature to
validateChildKeys(node) and updating every call site to pass a single argument.

That change removed several now-unused @param lines from the same file, but left
one behind on validateChildKeys:

/**
 * ...
 * @internal
 * @param {ReactNode} node Statically passed child of any type.
 * @param {*} parentType node's parent's type.   // <- no such parameter anymore
 */
function validateChildKeys(node) {

parentType no longer appears anywhere in the function signature or body, so this
@param line is stale and misleading to anyone reading the doc comment. This PR
deletes that single line. The remaining @param {ReactNode} node already fully and
correctly documents the sole parameter. No code or behavior change.

How did you test this change?

This is a documentation-only change (a JSDoc comment on an @internal helper), so
there is no runtime behavior to test. I verified it as follows:

• Confirmed parentType no longer appears anywhere in
  packages/react/src/jsx/ReactJSXElement.js (grep -n parentType returns no
  matches after the change).
• Confirmed the signature function validateChildKeys(node) and all call sites are
  unchanged by this diff.
• yarn prettier (via scripts/prettier/index.js check-changed) - clean.
• yarn linc (ESLint on changed files) - passed.
• yarn flow dom-node - No errors.

Diff (for reference)

diff --git a/packages/react/src/jsx/ReactJSXElement.js b/packages/react/src/jsx/ReactJSXElement.js
@@ -860,7 +860,6 @@ export function cloneElement(element, config, children) {
   *
   * @internal
   * @param {ReactNode} node Statically passed child of any type.
- * @param {*} parentType node's parent's type.
   */
 function validateChildKeys(node) {