[5.4][PHP8.5] imagedestroy() function has been deprecated

[heelc29]

Summary of Changes

remove no longer needed imagedestroy()

In the migration of various extensions from resources to objects, a number of functions to close or free the resources became no-ops
imagedestroy() since the ext/gd migration in PHP 8.0

https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_imagedestroy

Image::destroy() can be deprecated in future Joomla version (eg. 6.1)

Testing Instructions

Create scheduled task Image Size Check with manual execution and limit of eg. 50px

• enable max error reporting
• use php 8.5 (latest pre-version 8.5.0rc1)

Run task

Actual result BEFORE applying this Pull Request

Task status: Terminated
deprecation message (possibly further)

Expected result AFTER applying this Pull Request

Task status: Completed
no deprecation message about imagedestroy()

Link to documentations

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

The requested change has been implemented.

[muhme]

✅ Tested with JBT php8.5-rc

• Before the PR with 'Image Size Check' Scheduled Task seen PHP warning Function imagedestroy() is deprecated and task failed with JSON.parse: unexpected character at line 1 column 1 of the JSON data
• Applied patch with patchtester
  • ✅ no more Function imagedestroy() is deprecated
  • ✅ Scheduled Task 'Image Size Check' runs successful and one more image is reduced in size
• Switched to PHP 8.1
  • ✅ Scheduled Task 'Image Size Check' runs successful and one more image is reduced in size

[muhme]

Thank you @heelc29 for your contribution. Thank you @QuyTon and @HLeithner for your code reviews.