it was actually removed in 5.0,
commit 68a86dc1 (numa: remove deprecated -mem-path fallback to anonymous RAM)
clean up forgotten remnants in docs.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200911084410.788171-3-imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>