graph legend: minor refactor

public/app/plugins/panel/graph/Legend/Legend.tsx

 import _ from 'lodash';
-import React from 'react';
+import React, { PureComponent } from 'react';
 import { TimeSeries } from 'app/core/core';
 import CustomScrollbar from 'app/core/components/CustomScrollbar/CustomScrollbar';
 import { LegendItem, LEGEND_STATS } from './LegendSeriesItem';
@@ -61,7 +61,7 @@ interface LegendState {
   hiddenSeries: { [seriesAlias: string]: boolean };
 }
 
-export class GraphLegend extends React.PureComponent<GraphLegendProps, LegendState> {
+export class GraphLegend extends PureComponent<GraphLegendProps, LegendState> {
   static defaultProps: Partial<GraphLegendProps> = {
     values: false,
     min: false,
@@ -205,7 +205,7 @@ export class GraphLegend extends React.PureComponent<GraphLegendProps, LegendSta
   }
 }
 
-class LegendSeriesList extends React.PureComponent<LegendComponentProps> {
+class LegendSeriesList extends PureComponent<LegendComponentProps> {
   render() {
     const { seriesList, hiddenSeries, values, min, max, avg, current, total } = this.props;
     const seriesValuesProps = { values, min, max, avg, current, total };
@@ -225,7 +225,7 @@ class LegendSeriesList extends React.PureComponent<LegendComponentProps> {
   }
 }
 
-class LegendTable extends React.PureComponent<Partial<LegendComponentProps>> {
+class LegendTable extends PureComponent<Partial<LegendComponentProps>> {
   onToggleSort = stat => {
     let sortDesc = this.props.sortDesc;
     let sortBy = this.props.sort;
@@ -289,7 +289,7 @@ interface LegendTableHeaderProps {
   onClick?: (statName: string) => void;
 }
 
-class LegendTableHeaderItem extends React.PureComponent<LegendTableHeaderProps & LegendSortProps> {
+class LegendTableHeaderItem extends PureComponent<LegendTableHeaderProps & LegendSortProps> {
   onClick = () => this.props.onClick(this.props.statName);
 
   render() {
@@ -303,7 +303,7 @@ class LegendTableHeaderItem extends React.PureComponent<LegendTableHeaderProps &
   }
 }
 
-export class Legend extends React.PureComponent<GraphLegendProps> {
+export class Legend extends PureComponent<GraphLegendProps> {
   render() {
     return (
       <CustomScrollbar>

public/app/plugins/panel/graph/Legend/LegendSeriesItem.tsx

-import React from 'react';
+import React, { PureComponent } from 'react';
 import classNames from 'classnames';
 import { TimeSeries } from 'app/core/core';
 import { SeriesColorPicker } from 'app/core/components/colorpicker/SeriesColorPicker';
@@ -29,7 +29,7 @@ interface LegendItemState {
   yaxis: number;
 }
 
-export class LegendItem extends React.PureComponent<LegendItemProps, LegendItemState> {
+export class LegendItem extends PureComponent<LegendItemProps, LegendItemState> {
   static defaultProps = {
     asTable: false,
     hidden: false,
@@ -119,7 +119,7 @@ interface LegendSeriesLabelProps {
   onLabelClick?: (event) => void;
 }
 
-class LegendSeriesLabel extends React.PureComponent<LegendSeriesLabelProps & LegendSeriesIconProps> {
+class LegendSeriesLabel extends PureComponent<LegendSeriesLabelProps & LegendSeriesIconProps> {
   static defaultProps = {
     yaxis: undefined,
     onLabelClick: () => {},
@@ -158,7 +158,7 @@ function SeriesIcon(props) {
   return <i className="fa fa-minus pointer" style={{ color: props.color }} />;
 }
 
-class LegendSeriesIcon extends React.PureComponent<LegendSeriesIconProps, LegendSeriesIconState> {
+class LegendSeriesIcon extends PureComponent<LegendSeriesIconProps, LegendSeriesIconState> {
   static defaultProps = {
     yaxis: undefined,
     onColorChange: () => {},