win: fix and document VStudio license removal

Before this commit, license deletion used `reg delete .. /va /f`, which
deletes all valued under a key. However, the license data did not exist
under the specified subkeys, making the logic ineffective. This commit
changes it to delete the license registry key completely to correctly
remove the license data.

Changes:

- Change `reg delete /va` to delete the correct registry data.
- Create shared function for deleting license data for better
  maintainability.
- Add comment in generated script code for license removal.
- Add documentation for the scripts.
- Include a missing script to clear Visual Studio 2013 telemetry.
- Remove redundant lines of code in `CreateRegistryKey` and
  `DeleteRegistryKey` that initialize an unused variable.