DM: don't redirect stderr to verbose.log

verbose.log is currently tricky to get to, so it's hurting more than it
helps to direct stderr there.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178583002

Review-Url: https://codereview.chromium.org/2178583002
diff --git a/dm/DM.cpp b/dm/DM.cpp
index cccc92b..d931a9a 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -1265,7 +1265,7 @@
         gVLog = stderr;
     } else if (!FLAGS_writePath.isEmpty()) {
         sk_mkdir(FLAGS_writePath[0]);
-        gVLog = freopen(SkOSPath::Join(FLAGS_writePath[0], "verbose.log").c_str(), "w", stderr);
+        gVLog = fopen(SkOSPath::Join(FLAGS_writePath[0], "verbose.log").c_str(), "w");
     }
 
     JsonWriter::DumpJson();  // It's handy for the bots to assume this is ~never missing.