hardware: Remove '_numa_fit_instance_cell_with_pinning'

This somewhat arbitrary split out is unnecessarily confusing,
particularly when it doesn't involve any complicated logic and the bulk
of the pinning-specific logic instead occurs in
'_pack_instance_onto_cores'. Fold it back into its caller.

Part of blueprint use-pcpu-and-vcpu-in-one-instance

Change-Id: Ia651cf9f51ff7265c5e3bfec79bc695aa3fe3394
Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin