If the resulting geometry from applying a geometry nodes modifier contains
no mesh, give an error message "Evaluated geometry from modifier does not
contain a mesh". This gives people something to search and makes the behavior
more purposeful.

Also remove the modifyMesh implementation from the geometry nodes modifier,
since it isn't necessary anymore. And remove the existing "Modifier returned error,
skipping apply" message which was cryptic and redundant if applying returns
an actual error message.

Resolves T103229