Investigate need to feature check cancel and close events.

[nhunzaker]

The ReactBrowserEventEmitter checks for browser support of the cancel and close events. before attaching those listeners.

I'm curious why this is necessary. Did we need it for IE8?

I'd like to:

• Determine if there are ramifications to removing these checks
• Add comments above those lines if these checks are necessary.
• Maybe eliminate isEventSupported.js this is needed to check for input in ChangeEventPlugin

[nhunzaker]

Assigning this to me as a part of #11550, but I'd greatly appreciate any insight.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution.

[stale]

Closing this issue after a prolonged period of inactivity. If this issue is still present in the latest release, please create a new issue with up-to-date information. Thank you!