There is only one InnoDB crash recovery subsystem.
Allocating recv_sys statically removes one level of pointer indirection
and makes code more readable, and removes the awkward initialization of
recv_sys->dblwr.

recv_sys_t::create(): Replaces recv_sys_init().

recv_sys_t::debug_free(): Replaces recv_sys_debug_free().

recv_sys_t::close(): Replaces recv_sys_close().

recv_sys_t::add(): Replaces recv_add_to_hash_table().

recv_sys_t::empty(): Replaces recv_sys_empty_hash().