Move gn source files from patch

Auditors: @darkdh

Author: bbondy

browser/extensions/BUILD.gn

@@ -2,6 +2,8 @@ import("//build/config/features.gni")
 
 source_set("extensions") {
   sources = [
+    "api/brave_shields_api.cc",
+    "api/brave_shields_api.h",
     "brave_component_extension_resource_manager.cc",
     "brave_component_extension_resource_manager.h",
     "brave_component_loader.cc",