Using explicit Euler Forward in Recovery Kernel

As calling functions is not possible anymore with new implementation

tests/test_advection.py

@@ -157,7 +157,9 @@ def DeleteParticle(particle, fieldset, time):
 
     def SubmergeParticle(particle, fieldset, time):
         particle.depth = 0
-        AdvectionRK4(particle, fieldset, time)  # perform a 2D advection because vertical flow will always push up in this case
+        (u1, v1) = fieldset.UV[particle]
+        particle.lon += u1 * particle.dt  # noqa
+        particle.lat += v1 * particle.dt  # noqa
         particle.time = time + particle.dt  # to not trigger kernels again, otherwise infinite loop
         particle.set_state(StateCode.Success)