Hartmut is no longer with IBM and has not worked on GCC for a
long time; he asked to be removed from MAINTAINERS.
ChangeLog:
* MAINTAINERS: Remove Hartmut Penner as s390 maintainer.
rs6000/powerpc port Segher Boessenkool <segher@kernel.crashing.org>
rs6000 vector extns Aldy Hernandez <aldyh@redhat.com>
rx port Nick Clifton <nickc@redhat.com>
-s390 port Hartmut Penner <hepenner@us.ibm.com>
s390 port Ulrich Weigand <uweigand@de.ibm.com>
s390 port Andreas Krebbel <krebbel@linux.ibm.com>
sh port Alexandre Oliva <aoliva@gcc.gnu.org>