[codegen/node] Remove empty types files

[RobbieMcKinstry]

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Issue details

When reviewing #10831, @t0yv0 noticed namespaces with no types emit as empty files. In particular, here are the optimizations we intend:

1. Leaf namespaces with no types should not emit types files (/types/<leaf>/{input, output}.ts) when there aren't any types defined in those files. I.e. if input.ts is empty, it should be removed. If output.ts is empty, it should be removed.
2. Internal namespaces with no types in either input.ts or output.ts should be removed.

This improvement will eliminate 3005 files from Azure Native (improving performance by reducing total work).

Affected area/feature