message: core: remove ERROR define
  The cURL headers leave a define for ERROR which causes compile errors on
  Windows.
diff: #include <curl/curl.h>
  #include <curl/easy.h>
  +
  +// On Windows the build fails if a define for ERROR is leaked after
  +// above includes.
  +//
  +// The compile error is:
  +// "illegal token on right side of '::'"
  +// in Camera::Result::ERROR.
  +#ifdef ERROR
  +#undef ERROR
  +#endif
  