Move "Web Search" locator filter from Help to Core

It was invented as a "remote help" filter, but it actually doesn't have
anything to do with help or documentation.
Move it to more general place, also to enable future generalization to
another custom filter type.

Change-Id: Ib80eacd3c7cc33ae9f4d9353fa820272e3b0b25f
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/help/helpplugin.cpp

@@ -39,7 +39,6 @@
 #include "helpwidget.h"
 #include "localhelpmanager.h"
 #include "openpagesmanager.h"
-#include "remotehelpfilter.h"
 #include "searchtaskhandler.h"
 #include "searchwidget.h"
 #include "topicchooser.h"
@@ -155,7 +154,6 @@ public:
     LocalHelpManager m_localHelpManager;
 
     HelpIndexFilter helpIndexFilter;
-    RemoteHelpFilter remoteHelpFilter;
 };
 
 static HelpPluginPrivate *dd = nullptr;
@@ -281,9 +279,6 @@ HelpPluginPrivate::HelpPluginPrivate()
     connect(&helpIndexFilter, &HelpIndexFilter::linksActivated,
             this, &HelpPluginPrivate::showLinksInCurrentViewer);
 
-    connect(&remoteHelpFilter, &RemoteHelpFilter::linkActivated,
-            this, &QDesktopServices::openUrl);
-
     QDesktopServices::setUrlHandler("qthelp", HelpManager::instance(), "showHelpUrl");
     connect(ModeManager::instance(), &ModeManager::currentModeChanged,
             this, &HelpPluginPrivate::modeChanged);