MLECO-3187: Remove NPU op inclusion checks

 * If an optimized model is accidentally supplied with Ethos-U support
   disabled it will return from the model.Init() function before it gets
   to these checks so they are redundant.

Signed-off-by: Matthew Sloyan <matthew.sloyan@arm.com>
Change-Id: Ibe25531347ce29cb0866a9cc087c7267673ab4da