Removed SLICE_ALT from unittest/btree_metainfo.cc.
Removed SLICE_ALT from a bunch of memcached_btree files.
Removed SLICE_ALT in a whole bunch of places.
Removed SLICE_ALT frcom btree/backfill.cc.
Removed SLICE_ALT from btree/backfill.hpp
Removed SLICE_ALT from operations.tcc.