Remove smallestLabelSeparation from TimeScale (#3186)

Remove smallestLabelSeparation from TimeScale (#3186)

In case of charts with over 4000 points, smallestLabelSeparation
calculation contributes significantly to total cpu usage (about 25% according
to built-in Chrome profiler). Important thing to note is that result
of this calculation is not used at all.

Related commits:
  * 677c249b613bf1a4ebccb1bebda9f04f7346b866
    introduced smallestLabelSeparation. It was used in calculateBaseWidth
    function.
  * d198157fb8ea479ec9286bcf0ffb72e2e62e9661
    removed last use of smallestLabelSeparation. Since then the calculated
    value was never used.