src: remove unused and unimplemented method in env.h

Signed-off-by: gengjiawen <technicalcute@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/25699
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/env.h

@@ -646,7 +646,6 @@ class Environment {
 
   inline v8::Isolate* isolate() const;
   inline uv_loop_t* event_loop() const;
-  inline uint32_t watched_providers() const;
   inline void TryLoadAddon(const char* filename,
                            int flags,
                            std::function<bool(binding::DLib*)> was_loaded);