Fix v1 symupload protocol in Mac client.

- A printf's arguments got broken in refactor for v2 protocol (my fault).

Change-Id: I8018e25f55b18fd47038d28a4ff0ac3be3d2caae
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/2333387
Reviewed-by: Mark Mentovai <mark@chromium.org>

src/common/mac/HTTPMultipartUpload.m

@@ -59,7 +59,7 @@
 
   NSString* escaped = PercentEncodeNSString(key);
   NSString* fmt = @"Content-Disposition: form-data; name=\"%@\"\r\n\r\n%@\r\n";
-  NSString* form = [NSString stringWithFormat:fmt, boundary_, escaped, value];
+  NSString *form = [NSString stringWithFormat:fmt, escaped, value];
 
   [data appendData:[form dataUsingEncoding:NSUTF8StringEncoding]];
   return data;