Simplify process1.stripNone and improve process1.collect

While glancing again over `process1`, I noticed that `stripNone` can be simplified by using `collect`. I then [benchmarked](https://github.com/fthomas/scalaz-stream/blob/benchmarks/src/test/scala/scalaz/stream/performance/results.txt) this new implementation and it was slower than the original. So I improved the performance of `collect` and now `stripNone` is even slightly faster than the original. :fireworks: