Remove static from method

Having the method static was causing javah to change the signature of the native method which caused compiling errors

jme3-bullet/src/main/java/com/jme3/bullet/PhysicsSpace.java

@@ -995,7 +995,7 @@ public class PhysicsSpace {
         return solverNumIterations;
     }
     
-    private static native void setSolverNumIterations(long physicsSpaceId, int numIterations);
+    private native void setSolverNumIterations(long physicsSpaceId, int numIterations);
     
     public static native void initNativePhysics();