Update userguide .mod files: remove double declaration of beta

doc/userguide/models/Alt_Ex1.mod

@@ -8,7 +8,7 @@
 var y, c, k, a, h, b;
 varexo e,u;
 
-parameters beta, rho, beta, alpha, delta, theta, psi, tau;
+parameters beta, rho, alpha, delta, theta, psi, tau;
 
 alpha = 0.36;
 rho   = 0.95;