Legend toggle also applies hover effects on mobile devices

* **C3 version**: 0.6.12
* **D3 version**: 5.0.0
* **Browser**: All
* **OS**: All
* **Devices**: All **mobile** devices

* After toggling/tapping/clicking a disabled legend item, it also applies hover effect and grays out other bars/lines etc.

* You can reproduce this bug by using any sample on c3js.org which has more than one legend item.
For example:
* https://c3js.org/samples/chart_bar.html

* Reproduction steps(**on mobile device**):
1. Click(tap) one of the legend items to toggle it out (disable it).
2. Re-click(tap) same item.

* Expected result:
* All items on chart should be enabled.

* Actual result:
* Only the clicked(tapped) item is enabled because of hover effects.