AutoMerger: Remove extraneous flush

We already flush later in the body of commit(), which also has the
advantage of respecting the "save" bit.

Change-Id: I327b81c1b23caed938121687e73f086684176381

gerrit-server/src/main/java/com/google/gerrit/server/patch/AutoMerger.java

@@ -198,7 +198,6 @@ public class AutoMerger {
       builder.finish();
       treeId = dc.writeTree(ins);
     }
-    ins.flush();
 
     return commit(repo, rw, ins, refName, treeId, merge);
   }