wave equation: remove unnecessary del ops (#35)

Author: tkarna

examples/wave_equation.py

@@ -202,10 +202,6 @@ def step(u, v, e, u1, v1, e1, u2, v2, e2):
         v[:, 1:ny] = v[:, 1:ny] / 3.0 + 2.0 / 3.0 * (v2[:, 1:ny] + dt * dvdt)
         e[:, :] = e[:, :] / 3.0 + 2.0 / 3.0 * (e2[:, :] + dt * dedt)
 
-        del dudt
-        del dvdt
-        del dedt
-
     t = 0
     i_export = 0
     next_t_export = 0