Remove addStepEventListeners call

[RobbieTheWagner]

I am not 100% sure if removing this is okay or not. @chuckcarpenter do you know why we had this call here? Is addStepEventListeners only necessary when using modal mode?

Fixes #393

[chuckcarpenter]

Looks like this is just a port of the Ember add-on, so not sure otherwise: f1c4eeb

[RobbieTheWagner]

@chuckcarpenter addStepEventListeners is still called here

shepherd/src/js/modal.js

Line 105 in bef5342

addStepEventListeners.call(this);

I think this extra call was maybe to ensure some of the touchmove stuff was setup immediately or something? If you can't see anything in addStepEventListeners that we need to run in the tour constructor, I say we remove it.

[chuckcarpenter]

From my local testing in iOS and the docs site, this seems to work.