Some cleanups for https://github.com/fontforge/fontforge/pull/1843 and other

This has some other cleanups to bring down warning message sizes too
What name would you suggest?

I thought that the #define mentions fairly succinctly what the constant is for. I guess to could be tightened up by @see also type references, but I'd hoped that the uuid relationship in the same header file would be enough there.

I tried to avoid calling it FF_CZMQ_UUID_STRING_SIZE (or some CZMQ type thing) because there is always the chance that we swap out the UUID implemenation again in the future. An ascii serialization of a UUID is unlikely to change in length regardless of implementation though.