Many of the shipped icons were unused; clean them up.

Closed mchro requested to merge mchro/evince:iconcleanup into evince-next

I noticed that most of the icons were unused (I looked for usages of the macros defined, or the filenames being used elsewhere). I decided to try and clean it up. Please consider if we also want to remove the last non-scalable icon from 16x16--32x32: x-office-presentation.png.

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