Remove usage of handle based UM APIs

There is still some code (test code, netsh) which uses handle based APIs. Since the fd based APIs are now implemented, the caller code should be changed to use fd based APIs. Once the handle based APIs are no longer used, they can be deleted.

Locate the remaining handle-based API calls in the test code and netsh, then compare each caller with the corresponding fd-based API. Verify that no handle-based usages remain before removing those APIs; the issue does not name specific files or tests.

Written by the indexing model from the issue text.