memtx: clarify tuples against given index in memtx_tx_snapshot_cleaner

Currently, we create `memtx_tx_snapshot_cleaner` for each index in read
view. However, we somewhy clarify all tuples against primary index in
all cleaners. As a result, secondary indexes work incorrectly in read
view when MVCC is enabled, we may even get a tuple with one key, but
a tuple with another key will be returned because it is clarified
against primary index and repsects its order - that's wrong because
all indexes have its own orders. Let's clarify tuples against given
index to fix this mistake.

Community Edition is not affected at all since it uses read view only
for making a snapshot - we use only primary indexes there.

Part of tarantool/tarantool-ee#939

NO_TEST=in EE
NO_CHANGELOG=in EE
NO_DOC=bugfix

(cherry picked from commit 835fadd)