s390/appldata: Remove unused appldata_sysctl_header variable

s390/appldata: Remove unused appldata_sysctl_header variable

allmodconfig with clang W=1 points out an unused global variable:

arch/s390/appldata/appldata_base.c:54:33: error: variable
 'appldata_sysctl_header' set but not used [-Werror,-Wunused-but-set-global]

Just remove the variable. There is no point in adding error handling for a
failing register_sysctl() call.

Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>