perf(ReplaySubject): remove unnecessary computation

[staltz]

Remove unnecessary call to _getEvents() in ReplaySubject's _next(). No apparent reason for doing this. All tests still pass after this commit.

Please merge PR #447 before merging this PR. When running the micro perf test for shareReplay after this commit is applied, we get this result:

node perf/micro share-replay
Testing against RxJS v 3.1.2
old shareReplay with immediate scheduler x 44,835 ops/sec ±16.27% (87 runs sampled)
new shareReplay with immediate scheduler x 92,828 ops/sec ±1.57% (92 runs sampled)
        107.05% faster than Rx v 3.1.2

I don't know why that line was there in ReplaySubject.ts. Seems to contribute nothing to the behavior of ReplaySubject.

[benlesh]

Blocked by #447

[staltz]

Blocked but #447 is now mergeable, so soon this should be as well.

[benlesh]

Merged with 488ac2e... thanks, @staltz