Broker pallet: fix interlacing (#2811)

With the current code, when a user interlaces their region, the end
result will be three regions in the state:
- the non-interlaced region
- first part of the interlaced region
- second part of the interlaced region

The existing implementation retains the non-interlaced region in the
state, leading to a problematic scenario:

1. User 1 acquires a region from the market.
2. User 1 then interlaces this region.
3. Subsequently, User 1 transfers one part of the interlaced regions to
User 2.
Despite this transfer, User 1 retains the ability to assign the entire
original non-interlaced region, which is inconsistent with the fact that
they no longer own one of the interlaced parts.

This PR resolves the issue by removing the original region, ensuring
that only the two new interlaced regions remain in the state.