Redundant line for setting the arrayfire backend.

[amanabt]

5c71deb

https://github.com/Balavarun5/DG_Maxwell/blob/5c71deba7742ef079cadf45512c9984bf769c695/dg_maxwell/wave_equation_2d.py#L6

This line is redundant because an arrayfire backed be being set again after few lines using the variable
params.backend. Also, the presence of this statement might be dangerous if the backend being set in params.backend is not cpu and will give you errors.