Skip most of _mesa_update_vao_derived_arrays if the VAO is not static.
Drivers need a separate codepath for this.

This increases performance by 7% with glthread and the game "torcs".

The reason is that glthread uploads vertices and sets vertex buffers
every draw call, so the overhead is very noticable. glthread doesn't
hide the overhead, because the driver thread is the busiest thread.

Part-of: <mesa!4314>