remove ptrinfo

Correct: ptrinfo is a debug-only function. Intended to be called from kgdb stubs or for local printk debugging tests. I think gdb even allows to call functions while it's stopped on a breakpoint.

I added it as an example what slab knows about it's objects - I have such test functions in my local files, but most developers don't know how slab tracks objects. It's reference code - I'm not sure if it belongs into the kernel or not.

--
Manfred