UploadPack: Do not retain commit body when checking wants

The commit body contains the commit message, which is not needed for
reachability checks.

Change-Id: Ie209c3b3f022579942f05b8b5d0625ce26400a5d
Signed-off-by: Jonathan Nieder <jrn@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java

@@ -1863,6 +1863,7 @@ public class UploadPack {
 
 		ObjectReader reader = up.getRevWalk().getObjectReader();
 		try (RevWalk walk = new RevWalk(reader)) {
+			walk.setRetainBody(false);
 			AsyncRevObjectQueue q = walk.parseAny(notAdvertisedWants, true);
 			try {
 				RevObject obj;