Fixes issue #1658: Field formatter trying to apply missing formatter

This pull requests closes #1658.

The code that used the `field` format functions from the `raw` object has been removed. Fixing the current bug will cause values in the legend for Bar, Line, and Area charts to be broken for time values. Instead of displaying human readable date formats, timestamps will be displayed instead. We will need to refactor the `histogram` data converter to send either label formatters or change the current `xAxisFormatter` to make it more general for any value type. For more details, see my comments in #1658.

I have also updated the formatters for the pie chart. The pie chart data converter sends field formatters for all of its data values, which means the pie legend values will be formatted appropriately.