[4.0] Remove duplicate buttons in installation

[Quy]

Pull Request for Issue #26412.

Summary of Changes

After customizing installation, there are duplicate buttons. Remove duplicate buttons.

Testing Instructions

Apply PR.
Reinstall.
Customize installation.
Click Skip button.

Expected result

Actual result

[SharkyKZ]

I have tested this item ✅ successfully on 8ecfc27

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[alikon]

I have tested this item ✅ successfully on 8ecfc27

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/27186.}

[alikon]

RTC

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[HLeithner]

2 is not always better then 1, thanks for fixing this.