unit tests: remove more unused exogenous variables

tests/deterministic_simulations/multiple_lead_lags/sim_exo_lead_lag.mod

 // Same model as sim_exo_lead_lag_aux_vars.mod, but no auxiliary variables to deal with leads and lags
 
 var c k z_forward z_backward;
-varexo x z_shock;
+varexo x;
 
 parameters alph gam delt bet aa;
 alph=0.5;

tests/deterministic_simulations/multiple_lead_lags/sim_lead_lag.mod

 // Same model as sim_lead_lag_aux_vars.mod, but no auxiliary variables to deal with leads and lags
 
 var c k z_forward z_backward;
-varexo x z_shock;
+varexo x;
 
 parameters alph gam delt bet aa;
 alph=0.5;

tests/moments/example1_var_decomp.mod

@@ -24,7 +24,7 @@
 
 
 var y, c, k, a, h, b;
-varexo e, u, junk;
+varexo e, u;
 
 parameters beta, rho, alpha, delta, theta, psi, tau;