SignedCapsulePkg: Replace include guards with #pragma once

Replace traditional `#ifndef`/`#define`/`#endif` include guards with
`#pragma` once.

`#pragma once` is a widely supported preprocessor directive that
prevents header files from being included multiple times. It is
supported by all toolchains used to build edk2: GCC, Clang/LLVM, and
MSVC.

Compared to macro-based include guards, `#pragma once`:

- Eliminates the risk of macro name collisions or copy/paste errors
  where two headers inadvertently use the same guard macro.
- Eliminate inconsistency in the way include guard macros are named
  (e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.).
- Reduces boilerplate (three lines replaced by one).
- Avoids polluting the macro namespace with guard symbols.
- Can improve build times as the preprocessor can skip re-opening the
  file entirely, rather than re-reading it to find the matching
  `#endif` ("multiple-include optimization").
  - Note that some compilers may already optimize traditional include
    guards, by recognzining the idiomatic pattern.

This change is made acknowledging that overall portability of the
code will technically be reduced, as `#pragma once` is not part of the
C/C++ standards.

However, this is considered acceptable given:

1. edk2 already defines a subset of supported compilers in
   BaseTools/Conf/tools_def.template, all of which have supported
   `#pragma once` for over two decades.
2. There have been concerns raised to the project about inconsistent
   include guard naming and potential macro collisions.

Approximate compiler support dates:

- MSVC: Supported since Visual C++ 4.2 (1996)
- GCC: Supported since 3.4 (2004)
  (http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html)
- Clang (LLVM based): Since initial release in 2007

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

SignedCapsulePkg/Include/Guid/EdkiiSystemFmpCapsule.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef __EDKII_SYSTEM_FMP_CAPSULE_GUID_H__
-#define __EDKII_SYSTEM_FMP_CAPSULE_GUID_H__
+#pragma once
 
 /**
   @verbatim
@@ -142,5 +141,3 @@ typedef struct {
 extern EFI_GUID  gEdkiiSystemFirmwareImageDescriptorFileGuid;
 extern EFI_GUID  gEdkiiSystemFmpCapsuleConfigFileGuid;
 extern EFI_GUID  gEdkiiSystemFmpCapsuleDriverFvFileGuid;
-
-#endif

SignedCapsulePkg/Include/Library/EdkiiSystemCapsuleLib.h

@@ -6,8 +6,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
-#ifndef __EDKII_SYSTEM_CAPSULE_LIB_H__
-#define __EDKII_SYSTEM_CAPSULE_LIB_H__
+#pragma once
 
 #include <Guid/EdkiiSystemFmpCapsule.h>
 
@@ -142,5 +141,3 @@ CapsuleAuthenticateSystemFirmware (
   OUT VOID    **AuthenticatedImage,
   OUT UINTN   *AuthenticatedImageSize
   );
-
-#endif

SignedCapsulePkg/Include/Library/IniParsingLib.h

@@ -24,8 +24,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
-#ifndef __INI_PARSING_LIB_H__
-#define __INI_PARSING_LIB_H__
+#pragma once
 
 /**
   Open an INI config file and return a context.
@@ -154,5 +153,3 @@ EFIAPI
 CloseIniFile (
   IN      VOID  *Context
   );
-
-#endif

SignedCapsulePkg/Include/Library/PlatformFlashAccessLib.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef __PLATFORM_FLASH_ACCESS_LIB_H__
-#define __PLATFORM_FLASH_ACCESS_LIB_H__
+#pragma once
 
 #include <Protocol/FirmwareManagement.h>
 
@@ -91,5 +90,3 @@ PerformFlashWriteWithProgress (
   IN UINTN                                          StartPercentage,
   IN UINTN                                          EndPercentage
   );
-
-#endif

SignedCapsulePkg/Universal/RecoveryModuleLoadPei/RecoveryModuleLoadPei.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _RECOVERY_MODULE_LOAD_PEI_H_
-#define _RECOVERY_MODULE_LOAD_PEI_H_
+#pragma once
 
 #include <PiPei.h>
 
@@ -33,5 +32,3 @@ typedef struct {
   UINTN       Length;
   UINTN       ImageOffset;
 } RECOVERY_CONFIG_DATA;
-
-#endif

SignedCapsulePkg/Universal/SystemFirmwareUpdate/SystemFirmwareDxe.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SYSTEM_FIRMWARE_UPDATE_H_
-#define _SYSTEM_FIRMWARE_UPDATE_H_
+#pragma once
 
 #include <PiDxe.h>
 
@@ -394,5 +393,3 @@ InitializePrivateData (
 extern EFI_GUID  gSystemFmpLastAttemptVariableGuid;
 extern EFI_GUID  mCurrentImageTypeId;
 extern EFI_GUID  gSystemFmpProtocolGuid;
-
-#endif