Revise F08 MPI_Wtime/Wtick to make buildiface simpler

No review since F08 binding is experimental now.

src/binding/fortran/use_mpi_f08/buildiface

@@ -33,10 +33,6 @@ while (<$mpi_f08_fh>) {
         $_ =~ s/subroutine\s+MPI_/subroutine PMPIR_/;
     } elsif (/function\s+MPI_/) {
         $_ =~ s/function\s+MPI_/function PMPIR_/;
-    } elsif (/MPI_Wtick_f08/) { # Replace return value
-        $_ =~ s/MPI_Wtick_f08/PMPIR_Wtick_f08/;
-    } elsif (/MPI_Wtime_f08/) { # Replace return value
-        $_ =~ s/MPI_Wtime_f08/PMPIR_Wtime_f08/;
     }
     print $pmpi_f08_fh $_;
 }

src/binding/fortran/use_mpi_f08/mpi_f08.F90

@@ -4090,16 +4090,16 @@ interface MPI_Ineighbor_alltoallw
 end interface MPI_Ineighbor_alltoallw
 
 interface MPI_Wtick
-    function  MPI_Wtick_f08()
+    function  MPI_Wtick_f08() result(res)
         implicit none
-        double precision :: MPI_Wtick_f08
+        double precision :: res
     end function MPI_Wtick_f08
 end interface MPI_Wtick
 
 interface MPI_Wtime
-    function MPI_Wtime_f08()
+    function MPI_Wtime_f08() result(res)
         implicit none
-        double precision :: MPI_Wtime_f08
+        double precision :: res
     end function MPI_Wtime_f08
 end interface MPI_Wtime