ArmPkg/ArmSoftFloatLib: remove source files that are no longer used

ArmPkg/ArmSoftFloatLib: remove source files that are no longer used

Now that we have switched to a new version of the SoftFloat code,
remove the source files that make up the old implementation, and
are no longer referenced.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1845
Acked-by: Jian J Wang <jian.j.wang@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>