Remove broken and obsolete VisualScript nodes

### Describe the project you are working on

General VisualScript improvements and learning c++

### Describe the problem or limitation you are having in your project

Considering it's better to have fewer but working vs_nodes I would like to delete a few broken and obsolete nodes.
1. As described in [PR 54663](https://github.com/godotengine/godot/pull/54663) `VisualScriptVariable...` is obsolete.
2. As described in [PR 48783](https://github.com/godotengine/godot/issues/48783) `VisualScriptSubCall` is not working.
3. `VisualScriptYieldSignal` is not working `VisualScriptYield` needs to be renamed to `await` to match GDScript. [Proposal 3036](https://github.com/godotengine/godot-visual-script/issues/5)

### Describe the feature / enhancement and how it helps to overcome the problem or limitation

Delete stuff

### Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Delete stuff

### If this enhancement will not be used often, can it be worked around with a few lines of script?

These vs_nodes are not being used often.

### Is there a reason why this should be core and not an add-on in the asset library?

Delete stuff