service/storage_proxy: get_max_result_size() defer to db for unlimited queries
service/storage_proxy: get_max_result_size() defer to db for unlimited queries

Defer picking the appropriate max result size for unlimited queries to
the database, which is already the place where we make query classifying
decisions. This move means that all these decisions are now centralized
in the database, not scattered in different places and fixing one fixes
all users.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla