OvmfPkg/SmmCpuFeaturesLib: drop obsolete API implementation

OvmfPkg/SmmCpuFeaturesLib: drop obsolete API implementation

Commit 0426115b6738 ("UefiCpuPkg: Remove unused API in
SmmCpuFeaturesLib.h", 2022-12-21) removed the declaration of the function
SmmCpuFeaturesAllocatePageTableMemory() from the "SmmCpuFeaturesLib.h"
library class header.

Remove the API's (null-)implementation from OvmfPkg/SmmCpuFeaturesLib as
well.

Testing: OVMF builds, boots, and suspends/resumes (see earlier in this
series).

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=4235
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>