Based on the details you've provided, I believe you've got two options here, both of which will require some level of custom XML:
1) Add a Trend line to your chart, which will require the removal of the 3rd series on your chart and the inclusion of some <axis_marker> tags under the y_axis section of your chart XML. You'll see the sample XML code outlined in AnyChart's User Guide, and I've also got an example in my Sample Application on apex.oracle.com, here.
2) Customise the <data> component of your chart XML, to remove the tooltips and labels from being displayed for the 3rd series of your chart. This option is more complex than option 1 above, so my recommendation would be to go with option 1. However, if option 1 doesn't meet your requirements, then you can take a look at another example in my Sample Application, here, where I offer a suggestion on how you could handle the customisation of your chart data.
I hope this helps.