OvmfPkg: remove Csm16

Csm16 is not used by any platform at this point, remove it.

This shrinks the list of resources scheduled for removal to:

- GUIDs (protocols or otherwise):
  - gEfiLegacy8259ProtocolGuid

- headers:
  - Protocol/Legacy8259.h

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=4588
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20231110235820.644381-31-lersek@redhat.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Corvin Köhne <corvink@FreeBSD.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

OvmfPkg/Csm/Csm16/Csm16.inf

@@ -1,17 +0,0 @@
-## @file
-#  CSM Binary
-#
-#  Copyright (c) 2006 - 2011, Intel Corporation. All rights reserved.<BR>
-#  SPDX-License-Identifier: BSD-2-Clause-Patent
-#
-##
-
-[Defines]
-  INF_VERSION                    = 0x00010005
-  BASE_NAME                      = Csm16
-  FILE_GUID                      = 1547B4F3-3E8A-4FEF-81C8-328ED647AB1A
-  MODULE_TYPE                    = USER_DEFINED
-  VERSION_STRING                 = 1.0
-
-[Binaries]
-  BIN|Csm16.bin|*

OvmfPkg/Csm/Csm16/ReadMe.txt

@@ -1,12 +0,0 @@
-This module allows a CSM16 binary to be easily included
-in the OVMF.fd output file.
-
-=== How to use Csm16.inf ===
-
-1. Copy the CSM16 binary to OvmfPkg/Csm/Csm16/Csm16.bin
-2. Build OVMF with CSM_ENABLE defined.
-
-   For example:
-   * build -D CSM_ENABLE, or
-   * OvmfPkg/build.sh -D CSM_ENABLE
-