KVM: x86: Delete documentation for READ|WRITE in KVM_X86_SET_MSR_FILTER

Delete the paragraph that describes the behavior when both
KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE are set for a range.  There is
nothing special about KVM's handling of this combination, whereas
explicitly documenting the combination suggests that there is some magic
behavior the user needs to be aware of.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220831001706.4075399-2-seanjc@google.com