UseOnce block does not get unlocked after transform

[hedgefield]

Issue Overview

Converting a locked UseOnce block to another block type does not remove the lock.

Steps to Reproduce (for bugs)

1. Add a subhead block.
2. Add another subhead block, this gets locked for violating UseOnce so to speak.
3. Use the block switcher to switch the locked subhead block to a paragraph block.
4. Now the error says "Paragraph cannot be used twice".

Chrome with WP 4.9.4 vagrant and Gutenberg 2.3.0.

Expected Behavior

The lock to be lifted after an acceptable transformation has been made (as in, to a block that does not trigger UseOnce).

Current Behavior

UseOnce is enforced until the block is deleted.

[mcsf]

@hedgefield, I was circling back to this one. Can you still repro?

[hedgefield]

Nope, it's fixed in 2.4! 🎉