Retire GUC parallel_hash_enable_motion_broadcast

[avamingli]

Cloudberry Database version

No response

What happened

Recently I'm working on parallel join refactor and found the 
GUC parallel_hash_enable_motion_broadcast.

It's added by history reasons as a workaround for POC.
We don't have exactly the right parallel feature at the time.
It's neither reasonable to keep it, nor we have test cases
for this wired GUC.
And we are not clear what the improvement is with it.
Retire it and keep codes same with UPSTREAM.

What you think should happen instead

No response

How to reproduce

No need.

Operating System

Ubuntu

Anything else

No response

Are you willing to submit PR?

• Yes, I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct.