Hisilicon/DS3231RealTimeClockLib: drop LibRtcVirtualNotifyEvent

The RealTimeClockLib class header in edk2 mistakenly declares a function
called LibRtcVirtualNotifyEvent(). No component ever calls this function
crossing module boundaries; all RealTimeClockLib instances in edk2 and
edk2-platforms are supposed to register (and do register) their
SetVirtualAddressMap() notification functions.

In particular, DS3231RealTimeClockLib *itself* doesn't even use
LibRtcVirtualNotifyEvent() -- the function is defined with an empty body,
clearly in an understandable, but misguided, attempt, to conform to the
(bogus) library interface. Remove the function.

Build-tested only (with the Hisilicon platforms).

Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Wenyi Xie <xiewenyi2@huawei.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=4564


Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>