Remove unneeded/breaking code, update camera example

[javl]

trafficstars

Thank you for this example, it was just what I needed to use my IP camera as a texture.

I did have some trouble finding a cross-platform alternative to System.Drawing.dll, but found out this include is not even used by the script. So this pull request removes that line, together with the unused public Bitmap bitmap { get; set; }. This way, the script works both on Windows and Linux (and probably MacOS as well).

I also updated the webcam example link to a new, functional source. I did not update the other files generated by Unity, as those will get updated by the user's latest Unity version anyway.