StandaloneMmPkg/Core: remove legacy boot support

Remove the support for booting 'legacy' (i.e., non-UEFI boot) OSes.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: "Yao, Jiewen" <jiewen.yao@intel.com>
Reviewed-by: Achin Gupta <achin.gupta@arm.com>

StandaloneMmPkg/Core/StandaloneMmCore.h

@@ -635,28 +635,6 @@ MmDriverDispatchHandler (
 
   @return Status Code
 
-**/
-EFI_STATUS
-EFIAPI
-MmLegacyBootHandler (
-  IN     EFI_HANDLE               DispatchHandle,
-  IN     CONST VOID               *Context,        OPTIONAL
-  IN OUT VOID                     *CommBuffer,     OPTIONAL
-  IN OUT UINTN                    *CommBufferSize  OPTIONAL
-  );
-
-/**
-  This function is the main entry point for an MM handler dispatch
-  or communicate-based callback.
-
-  @param  DispatchHandle  The unique handle assigned to this handler by MmiHandlerRegister().
-  @param  Context         Points to an optional handler context which was specified when the handler was registered.
-  @param  CommBuffer      A pointer to a collection of data in memory that will
-                          be conveyed from a non-MM environment into an MM environment.
-  @param  CommBufferSize  The size of the CommBuffer.
-
-  @return Status Code
-
 **/
 EFI_STATUS
 EFIAPI