Fix deletion of expanded range

[nemanja-tosic]

Context

In #4529, i wanted to have a single event.preventDefault() for the entire callback, but missed an early return. Here, I've put the preventDefault call back to where it was, and called it again from the onFlushed callback.

Issue
Fixes: #4546

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: 5b1ebca

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

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