um: remove ARCH_NO_PREEMPT_DYNAMIC

There's no such symbol and we currently don't have any of the
mechanisms to make boot-time selection cheap enough, so we can't
have HAVE_PREEMPT_DYNAMIC_CALL or HAVE_PREEMPT_DYNAMIC_KEY.

Remove the select statement.

Reported-by: Lukas Bulwahn <[e-mail]>
Fixes: cd01672d64a3 ("um: Enable preemption in UML")
Signed-off-by: Johannes Berg <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

arch/um/Kconfig

···
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_STRNCPY_FROM_USER
 	select ARCH_HAS_STRNLEN_USER
-	select ARCH_NO_PREEMPT_DYNAMIC
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_KASAN if X86_64
 	select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN