Redmine

Since r24266 (#43451), Redmine::Thumbnail.generate has used the MIME type of the source file to detect PDFs. Its fourth parameter, _is_pdf, has therefore been unused. It was kept only for backward compatibility, and TODO comments in the code say it should be removed in Redmine 7.0.

The attached patch removes this parameter:

• Redmine::Thumbnail.generate now takes three arguments: source, target and size.
• Attachment#thumbnail no longer passes is_pdf? to the method.
• The TODO comments about the deprecation are removed.

Plugins that call Redmine::Thumbnail.generate with four arguments will raise an ArgumentError after this change. They should drop the fourth argument.