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>