Remove legacy process termination for shell executor
What does this MR do?
Remove legacy process termination for shell executor
Why was this MR needed?
Remove the legacy process termination for the shell
executor. This feature flag was introduced in !1770 (merged) for #3376 (closed)
What's the best way to test this MR?
This is just deleting code.
What are the relevant issue numbers?
Closes #6413 (closed)