Remove inferior 64px psensor.png icon

[Cody Garver]

Right now psensor ships 2 icons that serve the same purpose at the same dimensions:

icons/hicolor/64x64/psensor.png & icons/hicolor/scalable/psensor.svg

The PNG should be deleted, it's inferior for 2 reasons.

First, it's flawed. It has a white background instead of transparent, which none of the smaller variants have. I think it was added accidentally, it looks really ugly in the dock. It's a giant white square.

Second, there's already an SVG that starts at 64x64. And it's an SVG so the quality is gonna be better.

There are probably other PNGs that could be deleted for the same reasons but I did not look closely.