Remove temporary iOS 11.3 fix

[alexreardon]

As a part of #413 and #416 we introduced an always active touchmove listener to get around a webkit bug. Once the bug is fixed in webkit I am keen to remove the hack.

Also, the hack was only to get touch dragging working again. Currently any other calls to event.preventDefault() will not do anything in webkit (eg mousemove is currently not being prevented during a mouse drag). This goes against our how we use DOM events guide.

When webkit is fixed we will be able to:

1. remove the workaround
2. have consistent event prevention on webkit browsers

[alexreardon]

The bug has been fixed in safari and should be released in iOS 12. Once that soaks for a few weeks we will remove the work around from our code

[alexreardon]

See the webkit bug for more info

[acampagna]

But there is a followup bug that needs to be fixed: https://bugs.webkit.org/show_bug.cgi?id=185656

[alexreardon]

I have included a smaller fix in 11.0.5 and 12.x

[alexreardon]

#1407