Remove the placeholder LWLockId in place of the removed FreeSpaceLock. As pointed out by ITAGAKI Takahiro, we split SInvalLock into two in 8.4, so to keep the numbers of the rest of the locks unchanged from 8.3, we don't need a placeholder.
Remove the placeholder LWLockId in place of the removed FreeSpaceLock.
As pointed out by ITAGAKI Takahiro, we split SInvalLock into two in 8.4,
so to keep the numbers of the rest of the locks unchanged from 8.3, we
don't need a placeholder.

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