remove another case of frame/child src mucking

Author: oreoshake

lib/secure_headers/headers/policy_management.rb

@@ -257,17 +257,11 @@ def populate_fetch_source_with_default!(original, additions)
           # Don't set a default if directive has an existing value
           next if original[directive]
           if FETCH_SOURCES.include?(directive)
-            original[directive] = default_for(directive, original)
+            original[directive] = original[DEFAULT_SRC]
           end
         end
       end
 
-      def default_for(directive, original)
-        return original[FRAME_SRC] if directive == CHILD_SRC && original[FRAME_SRC]
-        return original[CHILD_SRC] if directive == FRAME_SRC && original[CHILD_SRC]
-        original[DEFAULT_SRC]
-      end
-
       def source_list?(directive)
         DIRECTIVE_VALUE_TYPES[directive] == :source_list
       end