Make installed physfs work out-of-the box if it's built with SDL3 support

[madebr]

• I confirm that I am the author of this code and release it to the PhysicsFS project under the Zlib license. This contribution does not contain code from other sources, including code generated by a Large Language Model ("AI").

[sezero]

It is rumored that I'm not good with cmake, and I didn't test this, but if it works with both shared=1+static=0 and shared=0+static=1 combinations in addition to the default of both being 1, then it's OK by me.

[madebr]

It is rumored that I'm not good with cmake, and I didn't test this, but if it works with both shared=1+static=0 and shared=0+static=1 combinations in addition to the default of both being 1, then it's OK by me.

Haha.

I removed linking of SDL3::SDL3 info physfs-static in case people want more control to use a shared/static SDL3 library with physfs. The library won't be out-of-the box anymore and behave like the SDL satellite libraries.

For the satellite libraries, this is a natural behavior because your project is already using SDL3.
With physfs, it's possible to link against a physfs built with SDL3 support, but not use SDL3 yourself.

Then again, this probably does not matter as long as SDL3 support is not enabled by default.