Remove curlbuild include

Curl removed that header in 73a2fcea0b4adea6ba342cd7ed1149782c214ae3
([1])
http.cpp doesn't use anything from that header and compilation works for
fine with curl 7.54.1

Fixes #647
Ref:
[1]: 73a2fcea0b

src/utils/http.cpp

@@ -1,5 +1,4 @@
 #include <curl/curl.h>
-#include <curl/curlbuild.h>
 #include <curl/easy.h>
 #include <sstream>