i965: Delete brw_wm_prog_key::render_to_fbo and drawable_height.

i965: Delete brw_wm_prog_key::render_to_fbo and drawable_height.

Now that we handle flipping and other gl_FragCoord transformations
via a uniform, these key fields have no users.

This patch actually eliminates the associated recompiles.  The Tomb
Raider benchmark's minimum FPS increases from ~1 FPS to a reasonable
number.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>