Replace an obsolete function alias

* lisp/isearch.el (isearch-yank-x-selection):
* lisp/mouse-copy.el (mouse-drag-secondary-pasting)
(mouse-drag-secondary-moving):
* lisp/obsolete/mouse-sel.el (mouse-sel-get-selection-function):
Replace obsolete alias x-get-selection with gui-get-selection.

lisp/isearch.el

@@ -1924,8 +1924,8 @@ If search string is empty, just beep."
 (defun isearch-yank-x-selection ()
   "Pull current X selection into search string."
   (interactive)
-  (isearch-yank-string (x-get-selection))
-  ;; If `x-get-selection' returned the text from the active region,
+  (isearch-yank-string (gui-get-selection))
+  ;; If `gui-get-selection' returned the text from the active region,
   ;; then it "used" the mark which we should hence deactivate.
   (when select-active-regions (deactivate-mark)))
 

lisp/mouse-copy.el

@@ -177,7 +177,7 @@ put the point at one place, then click and drag over some other region."
 	    (mouse-copy-work-around-drag-bug start-event last-input-event))
 	;; Remember what we do so we can undo it, if necessary.
 	(setq mouse-copy-last-paste-start (point))
-	(insert (x-get-selection 'SECONDARY))
+	(insert (gui-get-selection 'SECONDARY))
 	(setq mouse-copy-last-paste-end (point)))
     (setq mouse-copy-last-paste-start nil)))
 
@@ -216,7 +216,7 @@ by johnh@ficus.cs.ucla.edu."
   (if (mouse-drag-secondary start-event)
       (progn
 	(mouse-kill-preserving-secondary)
-	(insert (x-get-selection 'SECONDARY))))
+	(insert (gui-get-selection 'SECONDARY))))
 )
 
 (provide 'mouse-copy)

lisp/obsolete/mouse-sel.el

@@ -315,7 +315,7 @@ is `interprogram-cut-paste'.")
 	(or (gui-selection-value)
 	    (bound-and-true-p x-last-selected-text-primary)
             gui--last-selected-text-primary)
-      (x-get-selection selection)))
+      (gui-get-selection selection)))
   "Function to call to get the selection.
 Called with one argument: