r_ambient: default to 0
In accordance with team vote 210 https://xonotic.org/teamvotes/210/
Closes xonotic#47 (moved)
Closes #2767 (closed)
This also improves compatibility with Q3* maps
DP defaults to r_ambient 0 so we can just remove these lines.
Also removed r_hdr_scenebrightness 1 because that's DP default.
Edited by bones_was_here