Drop support for eager PyOpenCL

There's so much junk code in grudge that accommodates PyOpenCL's inability to broadcast properly, and I'm kind of over it. Numpy still works for eager debugging, so this shouldn't be a big loss. Any objections?

Depends on:
- https://github.com/inducer/arraycontext/pull/235 (to preserve eager test mode)

cc @alexfikl @matthiasdiener @majosm @MTCam @anderson2981 @lukeolson