Remove unnecessary image default features from compiler

[task-jp]

The software-renderer feature only needs PNG/JPEG support by default, which is already provided by the workspace image dependency. Remove the explicit default features to reduce build dependencies (removes rav1e, ravif, etc). Users who need additional image formats can enable them via the image-default-formats feature.

[ogoffart]

The issue here is that the image-default-formats is only enabling the features for the runtime, but not for the compiler, in case of cross compilation.
Also, this might be a breaking change if anyone relied on this.

What is the motivation for this change?

[task-jp]

Thanks for your comment.

I wanted to reduce compile time by making support for less commonly used image formats (like AVIF) optional. But you're right - there could already be users relying on these formats, so introducing this as a breaking change without a migration path isn't a good idea.