KVM: Drop stale kvm_is_transparent_hugepage() declaration

kvm_is_transparent_hugepage() was removed in commit 205d76ff ("KVM:
Remove kvm_is_transparent_hugepage() and PageTransCompoundMap()") but its
declaration in include/linux/kvm_host.h persisted. Drop it.

Fixes: 205d76ff

 (""KVM: Remove kvm_is_transparent_hugepage() and PageTransCompoundMap()")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211018151407.2107363-1-vkuznets@redhat.com