src: remove unused PROTOCOL_JSON array

Overlooked when moving code around in commit 42da740 ("inspector: split
HTTP/WS server from the inspector".)

PR-URL: nodejs#10407
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

src/inspector_agent.cc

@@ -31,10 +31,6 @@ namespace {
 using v8_inspector::StringBuffer;
 using v8_inspector::StringView;
 
-static const uint8_t PROTOCOL_JSON[] = {
-#include "v8_inspector_protocol_json.h"  // NOLINT(build/include_order)
-};
-
 std::string GetProcessTitle() {
   // uv_get_process_title will trim the title if it is too long.
   char title[2048];