[Extensions] Remove JSONFeatureProvider, SimpleFeature::Parse

extensions/common/features/manifest_feature.cc

Index: extensions/common/features/manifest_feature.cc
diff --git a/extensions/common/features/manifest_feature.cc b/extensions/common/features/manifest_feature.cc
index 313142d6843e106c64fe5c35e4ff53af10b49ecb..4d36d5278d161f4eb8ff2ec9da5e99da50c73802 100644
--- a/extensions/common/features/manifest_feature.cc
+++ b/extensions/common/features/manifest_feature.cc
@@ -34,22 +34,4 @@ Feature::Availability ManifestFeature::IsAvailableToContext(
   return CreateAvailability(IS_AVAILABLE);
 }
 
-bool ManifestFeature::Validate(std::string* error) {
-  if (!SimpleFeature::Validate(error))
-    return false;
-
-  if (extension_types().empty()) {
-    *error = name() + ": Manifest features must specify at least one " +
-             "value for extension_types.";
-    return false;
-  }
-
-  if (!contexts().empty()) {
-    *error = name() + ": Manifest features do not support contexts.";
-    return false;
-  }
-
-  return true;
-}
-
 }  // namespace extensions