So you did not "remove" the spring from the shaft, you just "unhooked" it from the return arm? If so, that is very common practice, although some debate whether needed or not, I don't like to full-time load the servo by leaving it hooked onto the return arm. Frankly, cannot imagine a LHS talking anyone out of an on-board engine kill mechanism, whether electrical or mechanical, but it isn't "required" yet by anyone other than IMAA and then only for events. Psychologically, I like knowing I can stop that thing if something goes amiss in flight. Seeing a 100cc powered aerobat get "stuck" at nearly full throttle once was all I needed to ever become a believer in it.