Remove cJSON
We now have nlohmann_json and shouldn't need two JSON libraries in the codebase. cJSON has some silly C coding behaviors that ends up being caught by clang-tidy
(see !1850 (merged)).
@tjcorona Seems that it has become used outside cumulus again (I see usage in DateTimeZonePair, Remus bits. some model session IO, discrete session, and polygon session).