StandaloneMmPkg/StandaloneMmCoreEntryPoint: drop explicit SerialPortLib call

Sending DEBUG output to the serial port should only be done via
DebugLib calls, which is in charge of initializing the serial
port when appropriate. So drop the explicit SerialPortInitialize ()
invocation, and rely on normal constructor ordering to get the
serial port into the appropriate state at the right time.

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/Library/StandaloneMmCoreEntryPoint/AArch64/StandaloneMmCoreEntryPoint.c

@@ -232,9 +232,6 @@ _ModuleEntryPoint (
   VOID                                    *TeData;
   UINTN                                   TeDataSize;
 
-  Status = SerialPortInitialize ();
-  ASSERT_EFI_ERROR (Status);
-
   // Get Secure Partition Manager Version Information
   Status = GetSpmVersion ();
   if (EFI_ERROR (Status)) {