Remove funlen

What does this MR do?

Removes the funlen go linter

Why was this MR needed?

funlen has been a source of frustration for our team, and also for our community contributors. They do valuable work for us, but their contributions often fail the CI process just because they've added one line to a function we wrote, which we can't reasonably expect them to fix.

This type of linter generally isn't very reliable and tends to produce too many false positives to be included in automated CI processes, especially for open-source code that gets a lot of attention.

We've discussed removing it in the past (example: #27535 (closed)), but we couldn't come to an agreement. Since this is an easy change to reverse, it has basically zero risk, and it would greatly benefit our community contributors, I suggest that we bias for action and remove it.

What are the relevant issue numbers?

Closes #27535 (closed)