Revert "Support an optional type annotation on export default statement"

This reverts commit a6a8a96249.

src/services/breakpoints.ts

@@ -173,10 +173,6 @@ module ts.BreakpointResolver {
                         return textSpan(node, (<ThrowStatement>node).expression);
 
                     case SyntaxKind.ExportAssignment:
-                        if (!(<ExportAssignment>node).expression) {
-                            return undefined;
-                        }
-
                         // span on export = id
                         return textSpan(node, (<ExportAssignment>node).expression);