fix: ineffectiveness of the "Whole Day" and "Open End" checkbox in Event forms (#3243)

[cihanandac]

This changes fix the ineffectiveness of "Whole Day" and "Open End" checkboxes over the visibility of the "Event Starts" and "Event Ends" fields.

• When "Open End" is enabled, the "Event Ends" field disappears from the form.
• When "Whole Day" is enabled, the time values of the "Event Starts" and "Event Ends" disappear.

Fixes #3243

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[cihanandac]

@sneridagh Thank you for the comment; I understand your point. I will look into the PR you shared and will try to modify this PR accordingly.

[stevepiercy]

@cihanandac FYI, #6161 was superseded by #6181 which was merged.