s390x: uv-guest: remove duplicated checks

Removing some tests which are done at other points in the code
implicitly.

In lib/s390x/uc.c#setup_uv(void) the rc of the qui result is verified
using asserts.
The whole test is fenced by lib/s390x/uc.c#uv_os_is_guest(void) that
checks if SET and REMOVE SHARED is present.

Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>