fix: ensure the pointer-init class is removed when updating the "locked" state

[WilliamDASILVA]

The locking mechanism does not work as expected when unlocking an element.
This is due to the fact that both pointer-init and no-pointer classes are present on the element.
When unlocking and then locking the element, we expect the element to remain locked.

This PR ensures that pointer-init is removed along with the other classes to avoid conflict.

Reproduction in https://app.grapesjs.com/