transaction: clear callback instances after usage Prevents double usage and helps reduce reference cycles, which were observed to occur in `hg convert` and other scenarios where there are multiple transactions per process.

lock: clear postrelease hooks list after usage Post release hooks should only be called once. Setting the list to None after usage will prevent accidental usage after they are used. In addition, it is easy for reference cycles to sneak into hook functions. Clearing the hooks after usage helps prevent these cycles.

ui: drop template aliases by HGPLAIN Otherwise, scripting output could be suffered from user aliases.