Remove deprecated state properties

Due to obsolete get_state API method which will be completely removed in the future - unnecessary data related to global dynamic properties have been removed

• removed steem_per_mvest, usd_per_steem, sbd_per_steem, dgpo from db hive_state table
• removed methods related to querying hived for variable values
• updated pattern tests

This MR is a prerequisite to implement HAF-App based version of Hivemind.