Partially revert "InitStageRegistry.h: prepare macros for being used in another namespace"

Restore previous definition of NUM_INIT_STAGES (that does not contain inet::).
NUM_INIT_STAGES is used as inet::NUM_INIT_STAGES in Simu5G and potentially
other derived projects as well. If we added "inet::" to the definition now,
it would cause compile errors in Simu5G, requiring INET-version-dependent
code in it to fix. We better leave the original definition.

Author: avarga

src/inet/common/InitStageRegistry.h

@@ -68,7 +68,7 @@ class INET_API InitStage
 
 #define Define_InitStage_Dependency(source, target) EXECUTE_PRE_NETWORK_SETUP(inet::InitStageRegistry::getInstance().addInitStageDependency(#source, #target))
 
-#define NUM_INIT_STAGES inet::InitStageRegistry::getInstance().getNumInitStages()
+#define NUM_INIT_STAGES InitStageRegistry::getInstance().getNumInitStages()
 
 } // namespace inet