[PR] lib: remove window.event
[PR] lib: remove window.event

Summary:
Remove the non-standard `event` global. This frequently causes issues
in event handlers where parameter name is something like `e` or `ev`,
and you reference it as `event`. Flow happily thinks it is an `Event`
object, although your code will break completely on sane browsers that
don’t implement it, like Firefox.

For reference, the `event` global is a proprietary Microsoft Internet
Explorer property
(https://developer.mozilla.org/en-US/docs/Web/API/Window/event), that
just happens to be implemented by Chrome and Edge as well :(.
Closes https://github.com/facebook/flow/pull/5434

Reviewed By: mroch

Differential Revision: D6685390

Pulled By: ianobermiller

fbshipit-source-id: 6b2a5e1f5c6ab33bce5878c26090e6fcf9f8f919

AgentME/flow,mroch/flow,popham/flow,popham/flow,gabelevi/flow,samwgoldman/flow,nmote/flow,popham/flow,gabelevi/flow,JonathanUsername/flow,facebook/flow,mroch/flow,popham/flow,mroch/flow,samwgoldman/flow,nmote/flow,popham/flow,AgentME/flow,claudiopro/flow,facebook/flow,JonathanUsername/flow,claudiopro/flow,facebook/flow,JonathanUsername/flow,facebook/flow,popham/flow,samwgoldman/flow,jamesgpearce/flow,jamesgpearce/flow,gabelevi/flow,gabelevi/flow,jamesgpearce/flow,JonathanUsername/flow,mroch/flow,nmote/flow,AgentME/flow,nmote/flow,samwgoldman/flow,samwgoldman/flow,mroch/flow,claudiopro/flow,JonathanUsername/flow,gabelevi/flow,AgentME/flow,jamesgpearce/flow,mroch/flow,jamesgpearce/flow,gabelevi/flow,claudiopro/flow,mroch/flow,nmote/flow,jamesgpearce/flow,facebook/flow,popham/flow,AgentME/flow,samwgoldman/flow,samwgoldman/flow,gabelevi/flow,claudiopro/flow,jamesgpearce/flow,facebook/flow,JonathanUsername/flow,facebook/flow,JonathanUsername/flow,nmote/flow,nmote/flow