Removes workaround introduced in 8c4ef3caa6. This is no longer necessary
and autocorrect works fine without it since at least iOS 14.4.

Closes #118

Button had a menu which had an action which had a closure which strongly
referenced the sourceView which was the button itself.

The old ProfileHeaderView was being leaked, and it was still listening
to the preferencesDidChange notification, but crashing because its
delegate (and therefore MastodonController) had been dealloc'd.

CoreData lookups

not provided

Fixes #117