MVPrimaryIndex: make inner class MVStoreCursor static

Avoids needlessly storing implicit reference to outer class

h2/src/main/org/h2/mvstore/db/MVPrimaryIndex.java

@@ -368,7 +368,7 @@ public class MVPrimaryIndex extends BaseIndex {
     /**
      * A cursor.
      */
-    class MVStoreCursor implements Cursor {
+    static class MVStoreCursor implements Cursor {
 
         private final Session session;
         private final Iterator<Entry<Value, Value>> it;