Remove CreateEmptyExtension from extension_function_test_utils
because "extensions/common/test_util.h" has duplicate function.

BUG=394840

Review URL: https://codereview.chromium.org/569493003

Cr-Commit-Position: refs/heads/master@{#295541}
diff --git a/extensions/common/test_util.cc b/extensions/common/test_util.cc
index 4eacfa6..e7efeb02 100644
--- a/extensions/common/test_util.cc
+++ b/extensions/common/test_util.cc
@@ -20,15 +20,13 @@
 }
 
 scoped_refptr<Extension> CreateEmptyExtension() {
-  scoped_refptr<Extension> empty_extension(
-      ExtensionBuilder()
-          .SetManifest(
-               DictionaryBuilder().Set("name", "Test").Set("version", "1.0"))
-          .Build());
-  return empty_extension;
+  return ExtensionBuilder()
+      .SetManifest(
+           DictionaryBuilder().Set("name", "Test").Set("version", "1.0"))
+      .Build();
 }
 
-scoped_refptr<Extension> CreateExtensionWithID(const std::string& id) {
+scoped_refptr<Extension> CreateEmptyExtension(const std::string& id) {
   return ExtensionBuilder()
       .SetManifest(
            DictionaryBuilder().Set("name", "test").Set("version", "0.1"))