MdePkg/UefiLib: move InternalEmptyFunction to UefiLib.c

MdePkg/UefiLib: move InternalEmptyFunction to UefiLib.c

The InternalEmptyFunction() is currently only used by code in
"UefiNotTiano.c" -- "Library functions that abstract areas of conflict
between framework and UEFI 2.0.". In the next patches,
InternalEmptyFunction() will be used from "UefiLib.c" as well, hence
promote it to "general utility" status: move the function definition to
"UefiLib.c", and place the function declaration (which is already extern)
into "UefiLibInternal.h".

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>