Revert "GIT_SILENT: minor qstring optimization"

This reverts commit f96deb39aa.

This was anti-optimization.
QStringLiteral is a QString created at build time. Initialization of
QString with it has no overhead.
QLatin1String is 8 bit C string wrapper which needs run-time conversion
to 16 bit encoding used in QString.

src/ProcessInfo.cpp

@@ -141,7 +141,7 @@ QSet<QString> ProcessInfo::commonDirNames()
 
 QString ProcessInfo::formatShortDir(const QString &input) const
 {
-    if(input == QLatin1String("/")) {
+    if(input == QStringLiteral("/")) {
         return QStringLiteral("/");
     }