duplicate *events def in timeseries.js v0.9.0

There is an duplicate, identical, *events definition in timeseries.js.

Although this appears not to cause issues loading the module in any JS VM, it does break when trying to compile with google-closure-compiler in simple mode (v0.8.x is where the v0.9.0 release tag was taken from):

```d:/src/pond $ git checkout v0.8.x
Your branch is up to date with 'origin/v0.8.x'.
Switched to branch 'v0.8.x'
d:/src/pond $ npx google-closure-compiler --js=lib/lib/timeseries.js --compilation_level "SIMPLE"
npx: installed 29 in 2.717s
lib/lib/timeseries.js:524: ERROR - [JSC_DUPLICATE_CLASS_METHODS] Class contains duplicate method name "events"
524| *events() {
^^^^^^
```
The issue manifests itself when referencing the package with ClojureScript (which uses the google clojure compiler), and more specifically when using the rect-timeseries-charts npm module which depends on pondjs v0.9.0.

I assume the duplicate *events def was unintentional, and thus I would consider this an (almost harmless) "bug".

PR to follow.

duplicate:
https://github.com/esnet/pond/blob/1a873b7a6a8b7bdc74e576b048beda3b06a4dc9f/lib/lib/timeseries.js#L524-L528

first occurance:
https://github.com/esnet/pond/blob/1a873b7a6a8b7bdc74e576b048beda3b06a4dc9f/lib/lib/timeseries.js#L393-L397

Thanks