Update form_events.rst

EventSubscriberInterface::getSubscribedEvents() method is static.
Update form_events.rst

Remove extraneous quote.
bug #4031 Update form_events.rst (redstar504)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4031).

Discussion
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Update form_events.rst

EventSubscriberInterface::getSubscribedEvents() method is static.

Commits
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a716a28 Update form_events.rst
229cde3 Update form_events.rst