Remove repeated norm_inf calculation in bicgsolver. (#4205)

Author: ankithadas

Src/LinearSolvers/MLMG/AMReX_MLCGSolver.H

@@ -182,7 +182,6 @@ MLCGSolverT<MF>::solve_bicgstab (MF& sol, const MF& rhs, RT eps_rel, RT eps_abs)
         Saxpy(sol, alpha, p, 0, 0, ncomp, nghost); // sol += alpha * p
         Saxpy(r,  -alpha, v, 0, 0, ncomp, nghost); // r += -alpha * v
 
-        rnorm = norm_inf(r);
         rnorm = norm_inf(r);
 
         if ( verbose > 2 && ParallelDescriptor::IOProcessor() )