Remove cv_hal_minMaxIdx implementation

OpenCV 4.9 has a bug that cv_hal_minMaxIdx is called regardless of the number of channels in the image even though the interface has no way to pass the channel count to it. This means that having cv_hal_minMaxIdx implemented causes a bug. Once there's a stable fix in OpenCV then this functionality can be added again with a patch for earlier versions, but until then remove it.

Fixes issues #2 (closed), #3 (closed), #4 (closed), #5 (closed).