layers: Remove wrapping of GPU objects by loader and layers
Loader only wraps GPU objects for creating a layer chain. After layer activation
layers and loader use unwrapped gpu object returned by the driver.
This is a large simplification.
This fixes a nasty bug where layers intercepting entrypoints with gpu objects
but not all these entrypoints would fail. These would cause non-uniform
unwrapping of gpu objects by the time the driver was called with a gpu object.
Fixes issue in loader_get_icd where it was trying to compare a wrapped GPU
against a non-wrapped GPU.