thermal: remove MMWAVE from partial system power reference

Since MMWAVE power rail will be removed for SUB6 only sku (device without MMWAVE module),
remove this from partial system power reference.

Bug: 279698561
Test: Build and boot on device, verify device can boot to home and
thermal can launch
Change-Id: I39c3f468f6cda269a5cacce92d346c5b9848b13b
Signed-off-by: Peter (YM) <peterym@google.com>