Reduce number of commands in FeedManager#trim (#3989)

spec/lib/feed_manager_spec.rb

@@ -131,4 +131,17 @@ RSpec.describe FeedManager do
       end
     end
   end
+
+  describe '#push' do
+    it 'trims timelines if they will have more than FeedManager::MAX_ITEMS' do
+      account = Fabricate(:account)
+      status = Fabricate(:status)
+      members = FeedManager::MAX_ITEMS.times.map { |count| [count, count] }
+      Redis.current.zadd("feed:type:#{account.id}", members)
+
+      FeedManager.instance.push('type', account, status)
+
+      expect(Redis.current.zcard("feed:type:#{account.id}")).to eq FeedManager::MAX_ITEMS
+    end
+  end
 end