Revert of [cronet] Expose API to set experimental options

components/cronet/ios/cronet_environment.h

Index: components/cronet/ios/cronet_environment.h
diff --git a/components/cronet/ios/cronet_environment.h b/components/cronet/ios/cronet_environment.h
index a419c2b6a0fae8777a43f434bc3e11ef9ae8a582..59cb79627eaae374f1637f011f475303f506227b 100644
--- a/components/cronet/ios/cronet_environment.h
+++ b/components/cronet/ios/cronet_environment.h
@@ -91,10 +91,6 @@
     http_cache_ = http_cache;
   }
 
-  void set_experimental_options(const std::string& experimental_options) {
-    experimental_options_ = experimental_options;
-  }
-
   void SetHostResolverRules(const std::string& host_resolver_rules);
 
   void set_ssl_key_log_file_name(const std::string& ssl_key_log_file_name) {
@@ -138,7 +134,6 @@
   bool quic_enabled_;
   std::string quic_user_agent_id_;
   std::string accept_language_;
-  std::string experimental_options_;
   std::string ssl_key_log_file_name_;
   URLRequestContextConfig::HttpCacheType http_cache_;