Should link to EventHandler delegate docs

The event can only be handled by implementing a specifically named event handler method.
The docs should link to EventHandler delegate docs either as a see also or within the documentation text

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#### Document Details

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* ID: b5f75ce3-005e-44ed-3d4d-a26248b55bea
* Version Independent ID: d0b25b20-9eee-ae14-199e-c84e0f5f9c86
* Content: [SessionStateModule.End Event (System.Web.SessionState)](https://docs.microsoft.com/en-us/dotnet/api/system.web.sessionstate.sessionstatemodule.end?view=netframework-4.7.2)
* Content Source: [xml/System.Web.SessionState/SessionStateModule.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Web.SessionState/SessionStateModule.xml)
* Product: **.net**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **riande**