build: Bump minimum Qt version to 5.11.3

src/qt/guiutil.cpp

@@ -888,11 +888,7 @@ void PolishProgressDialog(QProgressDialog* dialog)
 
 int TextWidth(const QFontMetrics& fm, const QString& text)
 {
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 11, 0))
     return fm.horizontalAdvance(text);
-#else
-    return fm.width(text);
-#endif
 }
 
 void LogQtInfo()