docs: Remove 'master_inventory.yml'
docs: Remove 'master_inventory.yml'

Remove 'master_inventory.yml'. It has been replaced with
'docs/Config_Specification.rst' and 'docs/Inventory_Specification.rst'.

Sample configuration files have been added to the 'sample_configs'
directory.

Change-Id: Ic373f07566afba256a98232729af78162b977ea9

open-power-ref-design-toolkit/cluster-genesis,open-power-ref-design-toolkit/cluster-genesis