Remove redundant nullptr checks before deallocation

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

src/net.cpp

@@ -2753,7 +2753,6 @@ CNode::~CNode()
 {
     CloseSocket(hSocket);
 
-    if (pfilter)
     delete pfilter;
 }
 

src/qt/paymentrequestplus.cpp

@@ -194,7 +194,6 @@ bool PaymentRequestPlus::getMerchant(X509_STORE* certStore, QString& merchant) c
         qWarning() << "PaymentRequestPlus::getMerchant: SSL error: " << err.what();
     }
 
-    if (website)
     delete[] website;
     X509_STORE_CTX_free(store_ctx);
     for (unsigned int i = 0; i < certs.size(); i++)

src/qt/paymentserver.cpp

@@ -364,7 +364,6 @@ void PaymentServer::initNetManager()
 {
     if (!optionsModel)
         return;
-    if (netManager != nullptr)
     delete netManager;
 
     // netManager is used to fetch paymentrequests given in bitcoin: URIs