Replace get_local_storage_proxy() and get_local_storage_proxy() with
constructor-provided references. Some unneeded cases were removed.
Test: unit (dev)
Closes#9816
* github.com:scylladb/scylla:
migration_manager: replace uses of get_storage_proxy and get_local_storage_proxy with constructor-provided reference
migration_manager: don't keep storage_proxy alive during schema_check verb
mm: don't capture storage proxy shared_ptr during background schema merge
mm: remove stats on schema version get