schema: Drop column schedule_member.membership_hash

It's not needed by Web anymore.

schema/pgsql/schema.sql

@@ -111,7 +111,6 @@ CREATE TABLE schedule_member (
     timeperiod_id bigint NOT NULL REFERENCES timeperiod(id),
     contact_id bigint REFERENCES contact(id),
     contactgroup_id bigint REFERENCES contactgroup(id),
-    membership_hash bytea DEFAULT NULL,
 
     -- There is no PRIMARY KEY in that table as either contact_id or contactgroup_id should be allowed to be NULL.
     -- Instead, there are two UNIQUE constraints that prevent duplicate entries. Multiple NULLs are not considered to

schema/pgsql/upgrades/019.sql

@@ -0,0 +1 @@
+ALTER TABLE schedule_member DROP membership_hash;