bug#69387: 30.0.50; A string shouldn't be both a docstring and a return value

[Mattias Engdegård]

> I'm rowing back on the warning; it's probably more annoying than detecting 
> actual errors, so it's been dropped from the patch.

This seems safe and desirable enough and has now been pushed to master.
It allowed us to revert the work-around in cc-defs.el that silenced a 
doc-string working.