[5.3] clean phan leftover

[heelc29]

Summary of Changes

phan was replaced with phpstan in #43919
and removed from dependencies in #43925

this PR cleanups the leftover .phan folder

Testing Instructions

code review because it was only needed for development

Link to documentations

Please select:

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

[richard67]

I have tested this item ✅ successfully on 35c315e

Reviewed with success.

As the ".phan" folder was not in the ."gitignore" file, there is nothing to do for that file, and this PR is complete.

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[laoneo]

Thanks!