Remove unnecessary forward declaration in core_probes.pidl

WorkerInspectorProxy doesn't exist anymore.

Bug: N/A
Tbr: alph@chromium.org
Change-Id: I4523f9fee7320dc745969699590c3980fc952f35
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617057Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661249}

third_party/blink/renderer/core/probe/core_probes.pidl

@@ -57,7 +57,6 @@ interface CoreProbes {
   class FontCustomPlatformData;
   class FontFace;
   class HTMLDocumentParser;
-  class WorkerInspectorProxy;
   class XMLHttpRequest;
 
   void DidClearDocumentOfWindowObject([Keep] LocalFrame*);