Fix Android build issues and gRPC LB policy

src/core/plugin_registry/grpc_unsecure_plugin_registry.c

Index: src/core/plugin_registry/grpc_unsecure_plugin_registry.c
diff --git a/src/core/plugin_registry/grpc_unsecure_plugin_registry.c b/src/core/plugin_registry/grpc_unsecure_plugin_registry.c
index fe238b791de684e95fce1bbde7d2876105c08662..beeaefb11ef8d332091b00d13fdf6f61c875ec5a 100644
--- a/src/core/plugin_registry/grpc_unsecure_plugin_registry.c
+++ b/src/core/plugin_registry/grpc_unsecure_plugin_registry.c
@@ -43,14 +43,10 @@ extern void grpc_resolver_sockaddr_init(void);
 extern void grpc_resolver_sockaddr_shutdown(void);
 extern void grpc_load_reporting_plugin_init(void);
 extern void grpc_load_reporting_plugin_shutdown(void);
-extern void grpc_lb_policy_grpclb_init(void);
-extern void grpc_lb_policy_grpclb_shutdown(void);
 extern void grpc_lb_policy_pick_first_init(void);
 extern void grpc_lb_policy_pick_first_shutdown(void);
 extern void grpc_lb_policy_round_robin_init(void);
 extern void grpc_lb_policy_round_robin_shutdown(void);
-extern void census_grpc_plugin_init(void);
-extern void census_grpc_plugin_shutdown(void);
 
 void grpc_register_built_in_plugins(void) {
   grpc_register_plugin(grpc_chttp2_plugin_init,
@@ -63,16 +59,8 @@ void grpc_register_built_in_plugins(void) {
                        grpc_resolver_sockaddr_shutdown);
   grpc_register_plugin(grpc_load_reporting_plugin_init,
                        grpc_load_reporting_plugin_shutdown);
-  // The following lines are commented out in Chromium so that we don't
-  // introduce dependency on nanopb.
-  // grpc_register_plugin(grpc_lb_policy_grpclb_init,
-  //                      grpc_lb_policy_grpclb_shutdown);
   grpc_register_plugin(grpc_lb_policy_pick_first_init,
                        grpc_lb_policy_pick_first_shutdown);
   grpc_register_plugin(grpc_lb_policy_round_robin_init,
                        grpc_lb_policy_round_robin_shutdown);
-  // The following lines are commented out in Chromium so that we don't
-  // introduce dependency on nanopb.
-  // grpc_register_plugin(census_grpc_plugin_init,
-  //                      census_grpc_plugin_shutdown);
 }