Remove the unused codes in config handler

[Tao Li]

Brief Description
-----------------
In starlingx metal project, some codes are never be used，so we should remove them avoiding ambiguous.

For example the return statement in these methods as follows.

_config_handler
hbs_config_handler
mtc_config_handler
mtc_nfvi_handler
_nfvi_handler

Severity
--------
minor

Steps to Reproduce
------------------

Expected Behavior
------------------

Actual Behavior
----------------

Reproducibility
---------------

System Configuration
--------------------
STD system

Branch/Pull Time/Commit
-----------------------
master

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/669073

[Ghada Khalil (gkhalil)]

Low priority / not gating any starlingx release -- code cleanup; doesn't have any system impact

[OpenStack Infra (hudson-openstack)]

Change abandoned by Bart Wensley (<email address hidden>) on branch: master
Review: https://review.opendev.org/669073
Reason: This patch has been idle for more than six months. I am abandoning it to keep the review queue sane. If you are still interested in working on this patch, please unabandon it and upload a new patchset.

[Ramaswamy Subramanian (rsubrama)]

No progress on this bug for more than 2 years. Candidate for closure.

If there is no update, this issue is targeted to be closed as 'Won't Fix' in 2 weeks.

[Ramaswamy Subramanian (rsubrama)]

Changing the status to 'Won't Fix' as there is no activity.