Avoid overriding text control color in generic wxSearchCtrl

Although it's the same color the control already had, overriding it
can have unexpected consequences, such as overriding the text selection
colors with GTK3. Fixes invisible wxSearchCtrl selection with GTK3.

src/generic/srchctlg.cpp

@@ -332,6 +332,7 @@ bool wxSearchCtrl::Create(wxWindow *parent, wxWindowID id,
                                         m_cancelBitmap);
 
     SetBackgroundColour( m_text->GetBackgroundColour() );
+    m_text->SetBackgroundColour(wxColour());
 
     RecalcBitmaps();