AMDGPU: Remove hacky attribute deduction from AMDGPUAttributor

amdgpu-calls and amdgpu-stack-objects don't really belong as
attributes, and are currently a hacky way of passing an analysis into
the DAG. These don't really belong in the IR, and don't really fit in
with the other attributes. Remove these to facilitate inverting the
pass.

I don't exactly understand the indirect call test changes. These tests
are using calls which are trivially replacable with a direct call, so
I'm not sure what the point is.