Explain if'defed regions

src/libraries/Common/src/Roslyn/Hash.cs

@@ -20,6 +20,8 @@ internal static int Combine(int newKey, int currentKey)
 
 #if false
 
+        // Disabled as these helpers are not currently needed in the polyfill of 
+
         internal static int Combine(bool newKeyPart, int currentKey)
         {
             return Combine(currentKey, newKeyPart ? 1 : 0);

src/libraries/Common/src/Roslyn/MetadataHelpers.cs

@@ -36,6 +36,8 @@ internal static class MetadataHelpers
 
 #if false
 
+        // Disabled as these helpers are not currently needed in the polyfill of SyntaxValueProvider.ForAttributeWithMetadataName
+
         internal struct AssemblyQualifiedTypeName
         {
             internal readonly string TopLevelType;