Remove SpinLockFree() / S_LOCK_FREE()?

Hi,

We currently have
* bool SpinLockFree(slock_t *lock)
* Tests if the lock is free. Returns true if free, false if locked.
* This does *not* change the state of the lock.
and its underlying S_LOCK_FREE() operation:
*
* bool S_LOCK_FREE(slock_t *lock)
* Tests if the lock is free. Returns true if free, false if locked.
* This does *not* change the state of the lock.

They are currently unused and, as far as I can tell, have never been
used outside test code /asserts. We also don't currently implement them
in the spinlock fallback code:

bool
s_lock_free_sema(volatile slock_t *lock)
{
/* We don't currently use S_LOCK_FREE anyway */
elog(ERROR, "spin.c does not support S_LOCK_FREE()");
return false;
}

I also find the "free" in the name very confusing. Everytime I look at
them (which, I grant, is not that often), I have to think about what
they mean.

Thus: Let's just remove SpinLockFree() / S_LOCK_FREE()?

Greetings,

Andres Freund