Fix applying tippyOptions

[genadis]

tippy options are already applied at: https://github.com/shipshapecode/shepherd/blob/master/src/js/utils/general.js#L179

the deleted lines essentially do something like:

Object.assign({a: 'hello', b: 'bye'}, '400px')

which results in:

{0: "4", 1: "0", 2: "0", 3: "p", 4: "x", a: "hello", b: "bye"}

getVariables import not used (there is error at compile time)