[S390] remove redundant stack check option

Newer gcc versions offer an architecture-independent option to check
the stack size and warn if it reaches a certain limit. This option
already existed for s390 by using -mwarn-dynamicstack. Since one
stack check option is enough remove the s390 specific stack check
but keep the option that warns about dynamic stack usage because
that is not covered by the generic option.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>