Remove GPIO.cleanup() to support multi-instance

[robolize]

Please remove the call to "GPIO.cleanup()" in the initialization. With this line in the code, you cannot have more than one instance of the filament sensors functional at any time. I am running 2 printers from my octoprint setup. I could not get both to work until I commented out that line.
Also, this line is impacting other plugins which are trying to use the GPIO interface.

I was clued into this by an issue raised in another plugin here, kantlivelong/OctoPrint-PSUControl#176