glsl: Disable the new copy propagation pass until it gets fixed.

It apparently regressed a bunch of ES2 cases.

src/glsl/glsl_parser_extras.cpp

@@ -764,7 +764,7 @@ do_common_optimization(exec_list *ir, bool linked, unsigned max_unroll_iteration
    progress = do_if_simplification(ir) || progress;
    progress = do_discard_simplification(ir) || progress;
    progress = do_copy_propagation(ir) || progress;
-   progress = do_copy_propagation_elements(ir) || progress;
+   /*progress = do_copy_propagation_elements(ir) || progress;*/
    if (linked)
       progress = do_dead_code(ir) || progress;
    else