The residents of 20 Ocean Avenue were evicted last week from the bluffside Bolinas property, following a long battle with county code enforcement. The site is in the custody of a court-appointed receiver who has deemed all of the structures unsafe and unsalvageable and plans to demolish them in the next several weeks.   Ralph Garside, who purchased the property in 1978, and several other long-term tenants had hoped to rehabilitate the property.