Fix client-http.cxx compile errors with libcurl-7.55.

* client-http.cxx: Remove inclusion of <curl/curlbuild.h>, which doesn't
  exist in libcurl-7.55. We evidently weren't using it anyway.

Author: drsmith2

client-http.cxx

@@ -25,7 +25,6 @@ extern "C" {
 #include <string.h>
 #include <curl/curl.h>
 #include <curl/easy.h>
-#include <curl/curlbuild.h>
 #include <json-c/json.h>
 #include <sys/stat.h>
 }