libsdl-1.3 removal

[Felix Geyer]

Hi all,

I'd like to get libsdl-1.3 removed since we have libsdl2 in unstable now.
Unfortunately blender and openttd started depending on libsdl-1.3 because
libsdl-1.3-dev provides libsdl-dev. That seems like a bug to me in the first
place since we don't want to default to 1.3/2.0 yet.

So I'd propose to
- upload libsdl-1.3 to drop the Provides
- request binNMUs of blender and openttd
- request removal of libsdl1-3

Regards,
Felix