[Transmuter] Remove `join_pool` and `exit_pool` messages

[iboss-ptk]

We want to have taker fees controllable for transmuter, which it is if the swap happens through poolmanager module.

But join_pool and exit_pool for transmuter is practically a swap for/from alloyed, so removing these messages support forces any swap equivalences to non-existent and will have to go through poolmanager