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/libs/utils/declarationmacros.h

@@ -30,4 +30,3 @@
     Class &operator=(const Class&) = delete; \
     Class(Class&&) = delete; \
     Class &operator=(Class&&) = delete;
-