XWIKI-8016: Remove the Chart plugin

xwiki-platform-core/xwiki-platform-chart/pom.xml

.../xwiki-platform-chart/xwiki-platform-chart-plugin/pom.xml

...ugin/src/main/java/com/xpn/xwiki/plugin/charts/Chart.java

...ain/java/com/xpn/xwiki/plugin/charts/ChartCustomizer.java

.../src/main/java/com/xpn/xwiki/plugin/charts/ChartImpl.java

...main/java/com/xpn/xwiki/plugin/charts/ChartingPlugin.java

...n/java/com/xpn/xwiki/plugin/charts/ChartingPluginApi.java

...a/com/xpn/xwiki/plugin/charts/actions/ChartingAction.java

...xpn/xwiki/plugin/charts/exceptions/ChartingException.java

...in/charts/exceptions/ColumnIndexOutOfBoundsException.java

...n/xwiki/plugin/charts/exceptions/DataSourceException.java

...ki/plugin/charts/exceptions/EmptyDataSourceException.java

...xpn/xwiki/plugin/charts/exceptions/GenerateException.java

...ki/plugin/charts/exceptions/InvalidArgumentException.java

...xwiki/plugin/charts/exceptions/InvalidParamException.java

...ki/plugin/charts/exceptions/MissingArgumentException.java

.../plugin/charts/exceptions/MissingDataSourceException.java

...gin/charts/exceptions/MissingMandatoryParamException.java

...iki/plugin/charts/exceptions/NoHeaderColumnException.java

.../xwiki/plugin/charts/exceptions/NoHeaderRowException.java