This almost completely reverts
commit acd23da4 and
retains a safe optimization:

recv_sys_t::parse(): Remove any old redo log records for the
truncated tablespace, to free up memory earlier.
If recovery consists of multiple batches, then recv_sys_t::apply()
will must invoke recv_sys_t::trim() again to avoid wrongly
applying old log records to an already truncated undo tablespace.