use do_item_remove in lru crawler
use do_item_remove in lru crawler

the crawler was saving a few operations by directly freeing an item, but lets
use the normal code path instead. The assert looks to ensure item_free() was
actually called as we expected. Though I guess lots of people don't use the
debug binary...

emcconville/memcached,emcconville/memcached,emcconville/memcached,emcconville/memcached