Disable depth of field for better performance

This should improve performance noticeably.
While it's nice to have depth of field when aiming, the performance
impact on most hardware is too high to be worth it.

level/geometry/environment.tres

@@ -24,10 +24,6 @@ ssao_enabled = true
 ssao_intensity = 3.0
 ssao_light_affect = 0.59
 ssao_ao_channel_affect = 1.0
-dof_blur_far_enabled = true
-dof_blur_far_distance = 100.0
-dof_blur_far_transition = 50.0
-dof_blur_near_enabled = true
 glow_enabled = true
 glow_levels/3 = false
 glow_levels/4 = true