[6.2] Remove obsolete variable definition

[HLeithner]

Cleanup

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

Remove the $allowLegacyListeners definition in the Plugins since they will never checked
in the relevant function because of the implementation of the SubscriberInterface

Note: The deprecation notice for 7.0 is for the CMSPlugin class not for the subclass which might implement them.

Testing Instructions

Code Review

Actual result BEFORE applying this Pull Request

2FA Works

Expected result AFTER applying this Pull Request

2FA Works

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[joomdonation]

I have tested this item ✅ successfully on 58a3920

Code review + real tests with Fixed Code and Authentication Code by Email plugins.

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[laoneo]

I have tested this item ✅ successfully on 58a3920

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/47912.}

[alikon]

RTC

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[MacJoom]

Thank you!