[calls] message-source: Use pragma once instead of include guard

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit 3c327393690dca3faa1b584241cbf8a4054827f8
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Mon Dec 27 20:11:13 2021 +0100

    message-source: Use pragma once instead of include guard

 src/calls-message-source.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)
---
diff --git a/src/calls-message-source.h b/src/calls-message-source.h
index 57754fdd..844ec60f 100644
--- a/src/calls-message-source.h
+++ b/src/calls-message-source.h
@@ -22,8 +22,7 @@
  *
  */
 
-#ifndef CALLS_MESSAGE_SOURCE_H__
-#define CALLS_MESSAGE_SOURCE_H__
+#pragma once
 
 #include "util.h"
 
@@ -74,5 +73,3 @@ struct _CallsMessageSourceInterface
 
 
 G_END_DECLS
-
-#endif /* CALLS_MESSAGE_SOURCE_H__ */