Fix duplicate MPI tests run

mpi/GNUmakefile.in

@@ -21,7 +21,8 @@ SUBDIRS=
 
 all:
 
-check: check-recursive
+@STARPU_SIMGRID_FALSE@check: check-recursive
+@STARPU_SIMGRID_FALSE@	:
 
 # divide by 4 the number of jobs to run in parallel, since mpirun will start 4
 # processes in the tests and examples