Change the methods implemented by GraphicsMagickToolkit and required by GraphicsMagickToolkitInterface
The following methods implemented by `GraphicsMagickToolkit` and required by `GraphicsMagickToolkitInterface` should be removed. * `extensionFromImageFormat()` * `mimeTypeFromImageFormat()` * `imageFormatFromExtension()` `getFileExtension()` should be added as new `GraphicsMagickToolkitInterface` method.
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