Removed attributes that are already available through composition

[MennoVink]

The extensions and extras attributes are not needed when glTFProperty has already been composited into the type.
Additionally name is not needed when compositing glTFChildOfRootProperty instead.
Attributes index and texCoord are not needed when textureInfo has already been composited into the type.

[javagl]

This is related to (and I think it implicitly fixes) #2420

[bghgary]

Maybe check if this change works with glTF Tools for vscode, just in case.

[javagl]

^ This, but also check whether the output generated by https://github.com/CesiumGS/wetzel is still the same after the change (as this output is, in fact, a normative part of the spec...)

[aaronfranke]

As far as I can tell, it's completely redundant to have these properties repeated in every schema. We should get rid of them.