Remove unnecessary definitions of energy in AWAGun-TrackBack-1 test.

RegressionTests/AWAGun-TrackBack-1/AWAGun-TrackBack-1.in

@@ -15,13 +15,10 @@ REAL n_particles         = 1E4;      //Number of particles in simulation.
 REAL beam_bunch_charge   = 1e-9;      //Charge of bunch. (C)
 
 //Initial Momentum Calculation
-REAL Edes    = 1.4e-9; //initial energy in GeV
-REAL gamma   = (Edes+EMASS)/EMASS;
-REAL beta    = sqrt(1-(1/gamma^2));
-REAL P0      = 13.234 * EMASS;  // Inital z-momentum in the distribution file (GeV/c).
+REAL P0 = 13.234 * EMASS;  // Inital z-momentum in the distribution file (GeV/c).
 
 //Printing initial energy and momentum to terminal output.
-value , {Edes, P0, OPALVERSION};
+value , {P0, OPALVERSION};
 
 //----------------------------------------------------------------------------
 // RF photoinjector (Gun)