Remove data from Pivot Graph

This proposal employs formulas rather than a pivot table and pivot chart.
I assume that the issue you are having is similar to the pivot chart on the left of the attached file. I don't know of a way to make it display as you want because when "None" is removed as a category then the percentages reflect only Gold and Platinum.
The summary range on the right uses the following formulas.
For Category: =IFERROR(INDEX(Table1[Category],MATCH(0,INDEX(COUNTIF(K$2:K2,Table1[Category]),,),)),"")
For % Running Total: =IF(K3="","",SUM(L2,COUNTIFS(Table1[Category],K3)/COUNTA(Table1[Category])))
Note that the raw data in columns A:B is an Excel table so that the references to the Category column will change automatically as the table is expanded/contracted. (test by selecting cell B11 > press the Tab key > put a category into cell B12).
Note that "None" is not selected in the Horizontal Axis Labels area of the Select Data Source dialog box.
Let us know if you have any questions.