Use Project.NameKey in GitRepositoryManager

This simplifies all of the calling sites, where they have a
Project.NameKey on hand and would prefer not to invoke .get() to
convert it into a String.

Change-Id: If661fc07cff542a57af3c28f27ab401ce7b3a656
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-pgm/src/main/java/com/google/gerrit/pgm/ScanTrackingIds.java

@@ -116,7 +116,7 @@ public class ScanTrackingIds extends SiteProgram {
     final Project.NameKey project = change.getDest().getParentKey();
     final Repository git;
     try {
-      git = gitManager.openRepository(project.get());
+      git = gitManager.openRepository(project);
     } catch (RepositoryNotFoundException e) {
       return;
     }