Remove the 3 from the cmake variables

[madebr]

Let's remove the 3 inside the cmake configuration variables of all SDL satellite libraries.

For SDL3 satellite libraries, this incompatibility should not be an issue.

I would not remove the 2 from the SDL2 satellites as projects may depend on this.
If this is not an issue, we can still read the "2-variable" and use it as a hint.
An advantage of doing the change for 2 as well could be an uniform way of configuring SDL2 and 3 cmake projects.

wdyt?

[slouken]

Yes, yes please!

[slouken]

I don't think we need to use the 2 variable as a hint.