Remove image_transport plugins to reduce CPU usage

[7ayushgupta]

Currently image_transport publishes several versions of the image such as compressedDepth, theora. After spending a few hours trying to optimise the vision code, I think we can reduce the CPU usage if we turn off these plugins, since a major part of the load is handling the transport of these images.
This link contains what I intended to do, but there is currently nothing such as a disablePlugin feature in my PC.