i965: Delete a batch size assertion that isn't very useful.

i965: Delete a batch size assertion that isn't very useful.

This assertion prevents you from doing intel_batchbuffer_require_space
with a size so huge it won't fit in the batchbuffer.  This doesn't seem
like a common mistake, and I've never seen the assert to be useful.

Soon, I hope to have batches grow, at which point this won't make sense.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>