loader/cJSON: Prefix/mark static/remove symbols

loader/cJSON: Prefix/mark static/remove symbols

Prefixes the symbols that are used outside the file with `loader_` to
match the others. Marks symbols that are not used outside as static.
Removes the symbols that are not used at all.

Prevents conflicts with other libraries that might also use cjson.
This may cause issues if the internal checkout of cJSON is updated, in
that case, it may be simpler to just prefix all of cJSON's symbols with
`loader_cJSON_`.

Signed-off-by: Christopher Degawa <ccom@randomderp.com>