dont sort sockets on image node

When a multilayer exr is loaded into an image node in the compositor, the sockets are sorted alphabetically instead of keeping the order of the EXR file.

This is problematic because to keep the correct order, the exr layers must be prefixed with a number/letter to ensure when the image node opens the file, the socket order matches the socket order of the file output node that created the exr file.

This requirment for a naming convention to control order can lead to issues in 3rd party compositors with certain passes. For example the cryptomatte isn't read properly in AE unless the prefix is removed (I've just been told).