Wholesale conversion to #pragma once

Kudos to cgmb and https://github.com/cgmb/guardonce

Change-Id: Ifa8970734b8d43fd08c9260c645bdb0228633791
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/texteditor/blockrange.h

@@ -23,8 +23,7 @@
 **
 ****************************************************************************/
 
-#ifndef BLOCKRANGE_H
-#define BLOCKRANGE_H
+#pragma once
 
 namespace TextEditor {
 
@@ -58,5 +57,3 @@ private:
 };
 
 } // namespace TextEditor
-
-#endif // BLOCKRANGE_H