InfoBar: Fix inconsistent copy ctor/operator=

Detected by GCC9.

Change-Id: I527d6e4a306077b7cf77ec61222babe803e6b0da
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/infobar.h

@@ -55,7 +55,6 @@ public:
     };
 
     InfoBarEntry(Id _id, const QString &_infoText, GlobalSuppressionMode _globalSuppression = GlobalSuppressionDisabled);
-    InfoBarEntry(const InfoBarEntry &other) { *this = other; }
 
     using CallBack = std::function<void()>;
     void setCustomButtonInfo(const QString &_buttonText, CallBack callBack);