Remove test of the unsupported core.legacyHeaders variable

Long ago we stopped supporting the core.legacyHeaders variable,
as JGit (like C Git) stopped creating the new pack-style loose
objects, rendering this variable pointless.  The test is still
valid, it proves we write the standard loose object format for
a commit, but the variable assignment has no impact on the test
so drop it from the code.

Change-Id: I051336ada23033c05e86bbff73ae5d78a37b1640
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/T0003_Basic.java

@@ -345,11 +345,7 @@ public class T0003_Basic extends SampleDataRepositoryTestCase {
 		}
 	}
 
-	public void test009_CreateCommitOldFormat() throws IOException,
-			ConfigInvalidException {
-		writeTrashFile(".git/config", "[core]\n" + "legacyHeaders=1\n");
-		db.getConfig().load();
-
+	public void test009_CreateCommitOldFormat() throws IOException {
 		final Tree t = new Tree(db);
 		final FileTreeEntry f = t.addFile("i-am-a-file");
 		writeTrashFile(f.getName(), "and this is the data in me\n");