delete hightlight and downplay doc

[gitforhlp]

fix issues#185

[Ovilia]

@pissang Please help review this PR.

[pissang]

As @plainheart said, this change is only scoped to the sunburst series, it should be mentioned in the note

[pissang]

I was confused because highlight is new introduced since 5.0 and it should not be deprecated. So I just did some search in the code and it seems the warning log is wrong in https://github.com/apache/echarts/blob/master/src/chart/sunburst/sunburstAction.ts#L90

It should be.

deprecateReplaceLog('sunburstHighlight', 'highlight');

So we should change this warning log instead of changing the doc

[gitforhlp]

It is stated in the V5 upgrade document that this is discarded in the sunrise chart,please check again https://echarts.apache.org/handbook/zh/basics/release-note/v5-upgrade-guide#%E4%B8%8D%E5%86%8D%E6%8E%A8%E8%8D%90%E4%BD%BF%E7%94%A8%E7%9A%84-api

旭日图（sunburst）： 动作类型 highlight 已被弃用，请使用 sunburstHighlight 代替。 动作类型 downplay 已被弃用，请使用 sunburstUnhighlight 代替。 选项 series.downplay 已被弃用，请使用 series.blur 代替。 选项 series.highlightPolicy 已不适用，请使用 series.emphasis.focus 代替。

[Ovilia]

apache/echarts#17587 is following the right track. I think there should be no document changing required so I'm going to close this PR. Thanks for the help!