SilverSearcher: Fix widget construction if not available

Setting a layout on a widget only works after the old layout
has been destroyed. Otherwise it just refuses and prints out
a warning on the cmdline which in turn results in not
displaying the failure inside the UI and keeping the line
edit for the optional search options.

Change-Id: Id4ff4679d67b625a7248569f6debf1912dc5bcf0
Reviewed-by: Przemyslaw Gorszkowski <pgorszkowski@gmail.com>

src/plugins/silversearcher/findinfilessilversearcher.cpp

@@ -176,8 +176,6 @@ FindInFilesSilverSearcher::FindInFilesSilverSearcher(QObject *parent)
 
     setEnabled(isSilverSearcherAvailable());
     if (!isEnabled()) {
-        auto layout = new QHBoxLayout(m_widget);
-        layout->setMargin(0);
         QLabel *label = new QLabel(tr("Silver Searcher is not available on the system."));
         label->setStyleSheet("QLabel { color : red; }");
         layout->addWidget(label);