vinyl: do not reuse lsm objects during recovery from vylog

If an index was dropped and then recreated, then while replaying vylog
we will reuse vy_lsm_recovery_info object corresponding to it. There's
no reason why we do that instead of simply allocating a new object -
amount of memory saved is negligible, but the code looks more complex.
Let's simplify the code - whenever we see VY_LOG_CREATE_LSM, create a
new vy_lsm_recovery_info object and replace the old incarnation if any
in the hash map.