Ifdef to if typo fix (#3844)

* Revert "Use CallFnAfter instead of CallOnConditionKeep (#3841)"

This reverts commit 36890a0.

* ifdef to if

Author: ritvikrao

tests/charm++/periodic/periodic.C

@@ -34,7 +34,7 @@ class main : public CBase_main {
     delete msg;
 
     mProxy = thisProxy;
-    #ifdef CALL_FN_AFTER
+    #if CALL_FN_AFTER
     startTime = CkWallTimer();
     #else
     startTime = 0.0;