Base: Drop QString-std::string conversion functions from Tools

Convenience helpers function Tools::toStdString and Tools::fromStdString
were implemented for Qt4 or older to perform utf8 aware conversion as
QString::toStdString/QString::fromStdString were using toAscii/fromAscii
internally (see https://dreamswork.github.io/qt4/classQString.html).

Since Qt5 QString uses toUtf8/fromUTf8, which makes the helper functions
obsolete (see https://doc.qt.io/qt-5/qstring.html#fromStdString).

src/Mod/TechDraw/Gui/QGIWeldSymbol.cpp

@@ -28,7 +28,6 @@
 #endif
 
 #include <Base/Console.h>
-#include <Base/Tools.h>
 
 #include <Mod/TechDraw/App/DrawLeaderLine.h>
 #include <Mod/TechDraw/App/DrawTile.h>
@@ -254,7 +253,7 @@ void QGIWeldSymbol::drawTailText()
     if (!vp) {
         return;
     }
-    QString qFontName = Base::Tools::fromStdString(vp->Font.getValue());
+    QString qFontName = QString::fromStdString(vp->Font.getValue());
     int fontSize = QGIView::exactFontSize(vp->Font.getValue(),
                                           vp->FontSize.getValue());