Belatedly removing long-obsolete .NET tests for AndroidDriver
Adding support for SwitchTo().ParentFrame() in .NET bindings

This brings the .NET bindings into parity with other languages. Fixes
issue #7419.
Adding URL endpoint for switchToParentFrame

This allows consumers of the webdriver-server module to implement the
switchToParentFrame command. Note that this does **not** mean that the
command is automatically implemented in drivers that use this module; it
simply means that the driver will correctly understand the URL endpoint.
As an example, the IE driver should now properly return "command not
implemented" rather than "unknown command".