fix(ConditionalFormattingControl): icon color in dark mode

Author: msyavuz

superset-frontend/src/explore/components/controls/ConditionalFormattingControl/ConditionalFormattingControl.tsx

@@ -53,7 +53,6 @@ export const FormatterContainer = styled(OptionControlContainer)`
 
 export const CloseButton = styled.button`
   ${({ theme }) => css`
-    color: ${theme.colorIcon};
     height: 100%;
     width: ${theme.sizeUnit * 6}px;
     border: none;