server: use base64 function from lws

src/utils.h

@@ -28,9 +28,6 @@ int get_sig(const char *sig_name);
 // Open uri with the default application of system
 int open_uri(char *uri);
 
-// Encode text to base64, the caller should free the returned string
-char *base64_encode(const unsigned char *buffer, size_t length);
-
 #ifdef _WIN32
 char *strsep(char **sp, char *sep);
 const char *quote_arg(const char *arg);