Remove redundant nullptr checks before deallocation

Rationale:
* delete ptr is a no-op if ptr is nullptr

src/qt/paymentserver.cpp

@@ -364,8 +364,7 @@ void PaymentServer::initNetManager()
 {
     if (!optionsModel)
         return;
-    if (netManager != nullptr)
-        delete netManager;
+    delete netManager;
 
     // netManager is used to fetch paymentrequests given in bitcoin: URIs
     netManager = new QNetworkAccessManager(this);