sstables: avoid passing schema unnecessarily
sstables: avoid passing schema unnecessarily

for prepare_summary we can just pass the min interval as a parameter and
avoid having the schema do yet another hop. For sealing the summary, it
is completely unused and we can do away with it.

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla,kjniemi/scylla,avikivity/scylla,duarten/scylla,duarten/scylla,kjniemi/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,kjniemi/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla