tracker-extract: Update panasonic cameras' RAW images mimetype

Carlos Garnacho requested to merge wip/carlosg/panasonic-raw-images into master

This used to be image/x-panasonic-raw, but changed in

Keep up with this change, which avoids us from going through the generic image handler (GStreamer) and making life terrible to people with those cameras. Reported by jurf on IRC.

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