Fix PHPMD errors [#3196486]

Hi, when i execute phpmd command i got the following errors :

FILE: /project/app/modules/custom/image_styles_mapping/src/Controller/ImageStylesMappingController.php
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 193 | VIOLATION | Avoid using undefined variables such as '$order_column' which will lead to PHP notices.
 197 | VIOLATION | Avoid using undefined variables such as '$order_column' which will lead to PHP notices.
 200 | VIOLATION | Avoid using undefined variables such as '$order_column' which will lead to PHP notices.

FILE: /project/app/modules/custom/image_styles_mapping/src/Service/ImageStylesMappingService.php
------------------------------------------------------------------------------------------------
 344 | VIOLATION | Avoid unused local variables such as '$plugin_definition'.

Issue fork image_styles_mapping-3196486

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3196486-fix-phpmd-errors changes, plain diff MR !3
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