Remove unnecessary files from a Xonotic "low" build.

strip_xonotic_low.txt

user@host:% tree autobuild/
autobuild/
├── data
│   ├── xonotic-rsync-data-low.pk3
│   └── xonotic-rsync-maps-low.pk3
├── key_0.d0pk
└── xonotic-linux64-dedicated

1 directory, 4 files

user@host:$ du -h autobuild/
97M autobuild/data
105M    autobuild/

# ---------------------------------
# commands used to reduce pk3 file size:

zip -qd xonotic-rsync-data-low.pk3 'textures/*' 'sound/*' 'gfx/*' '*/*/*.jpg' '*/*.jpg'              
unzip -ql xonotic-rsync-data-low.pk3 | grep -Eo '[^ ]*\.(jpg|png|wav|ogg|dem)$' | \                
xargs -I@ zip -qd xonotic-rsync-data-low.pk3 @                                                      
zip -qd xonotic-rsync-maps-low.pk3 'textures/*' 'sound/*' 'gfx/*' 'env/*' '*/*/*.jpg' '*/*.jpg'     
unzip -ql xonotic-rsync-maps-low.pk3 | grep -Eo '[^ ]*\.(jpg|png|wav|ogg)$' | \                     
xargs -I@ zip -qd xonotic-rsync-maps-low.pk3 @