Fix "Mac: Stubborn tooltips when menu window is open" (#1408)

The fix extends to all platforms the check that doesn't post a tooltip window if
a menu window is active.
Therefore, virtual member function Fl_System_Driver::use_tooltip_timeout_condition()
is no longer necessary.

src/Fl_System_Driver.H

@@ -162,8 +162,6 @@ public:
   virtual const char *filename_name(const char *buf) {return buf;}
   // implement to support fl_open_uri()
   virtual int open_uri(const char * /*uri*/, char * /*msg*/, int /*msglen*/) {return 0;}
-  // the default implementation of use_tooltip_timeout_condition() may be enough
-  virtual int use_tooltip_timeout_condition() {return 0;}
   // the default implementation of use_recent_tooltip_fix() may be enough
   virtual int use_recent_tooltip_fix() {return 0;}
   // the default implementation of need_test_shortcut_extra() may be enough

src/Fl_Tooltip.cxx

@@ -205,10 +205,7 @@ void Fl_Tooltip::tooltip_timeout_(void*) {
       if (window) window->hide();
       Fl::remove_timeout(tooltip_hide_timeout);
     } else {
-      int condition = 1;
-// bugfix: no need to refactor
-      if (Fl::system_driver()->use_tooltip_timeout_condition()) condition = (Fl::grab() == NULL);
-      if ( condition ) {
+      if ( Fl::grab() == NULL ) {
         if (!window) window = new Fl_TooltipBox;
         // this cast bypasses the normal Fl_Window label() code:
         ((Fl_Widget *) window)->label(tip);

src/drivers/Unix/Fl_Unix_System_Driver.H

@@ -30,7 +30,6 @@ public:
                             int (*sort)(struct dirent **, struct dirent **),
                             char *errmsg=NULL, int errmsg_sz=0) FL_OVERRIDE;
   int open_uri(const char *uri, char *msg, int msglen) FL_OVERRIDE;
-  int use_tooltip_timeout_condition() FL_OVERRIDE {return 1;}
   int file_browser_load_filesystem(Fl_File_Browser *browser, char *filename, int lname, Fl_File_Icon *icon) FL_OVERRIDE;
   void newUUID(char *uuidBuffer) FL_OVERRIDE;
   char *preference_rootnode(Fl_Preferences *prefs, Fl_Preferences::Root root, const char *vendor,