Don't use ...dbh->errstr in error message

The error might not be due to DB error, and anyhow, the DB error has already
been displayed when it first occurred within $SubAttachment->Create(...).

Author: puck

lib/RT/Attachment.pm

@@ -190,7 +190,7 @@ sub Create {
                 Attachment    => $part,
             );
             unless ($id) {
-                $RT::Logger->crit("Attachment insert failed: ". $RT::Handle->dbh->errstr);
+                $RT::Logger->crit("Attachment subpart insert failed.");
                 return ($id);
             }
         }