[4.0] com_associations remove unused JHtml::sidebar

[travisrisner]

Remove references to unused sidebar elements in com_associations. Also fixed a syntax error with the echo statement for the table caption on the modal template.

[Quy]

I have tested this item ✅ successfully on 90e60ee

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[infograf768]

I have tested this item ✅ successfully on 17ce73a

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/25264.}

[infograf768]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/25264.}

[infograf768]

Thanks.

[infograf768]

While testing this, I found an error in the modal because I forgot to take into account forced items in my PR #21581

Please test #25278