OvmfPkg: SmbiosPlatformDxe: eliminate duplicate entry point validation

At this point all platforms that use OvmfPkg/SmbiosPlatformDxe in edk2,
namely ArmVirtQemu.dsc and OvmfPkg*.dsc, have been migrated to
SmbiosVersionLib. Therefore SmbiosPlatformDxe itself can forego verifying
QEMU's SMBIOS entry point; if SmbiosVersionLib's validation was
successful, it should just rely on that.

(Note that SmbiosPlatformDxe has a depex on EFI_SMBIOS_PROTOCOL, installed
by SmbiosDxe, containing SmbiosVersionLib, therefore the set/get order of
PcdQemuSmbiosValidated is ensured.)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Wei Huang <wei@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gabriel L. Somlo <somlo@cmu.edu>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18180 6f19259b-4bc3-4df7-8a09-765794883524