Fix typo in rcirc function name

* lisp/net/rcirc.el (rcirc-format-strike-through): Rename from
'rcirc-format-strike-trough'.  Make old name into obsolete
function alias.  Update all uses.

lisp/net/rcirc.el

@@ -1396,10 +1396,10 @@ inserted."
   (interactive "P")
   (rcirc-format "\^_" replace))
 
-(defun rcirc-format-strike-trough (replace)
-  "Insert strike-trough formatting.
+(defun rcirc-format-strike-through (replace)
+  "Insert strike-through formatting.
 If REPLACE is non-nil or a prefix argument is given, any prior
-formatting will be replaced before the strike-trough formatting
+formatting will be replaced before the strike-through formatting
 is inserted."
   (interactive "P")
   (rcirc-format "\^^" replace))
@@ -1421,7 +1421,7 @@ inserted."
   "C-c C-f C-b" #'rcirc-format-bold
   "C-c C-f C-i" #'rcirc-format-italic
   "C-c C-f C-u" #'rcirc-format-underline
-  "C-c C-f C-s" #'rcirc-format-strike-trough
+  "C-c C-f C-s" #'rcirc-format-strike-through
   "C-c C-f C-f" #'rcirc-format-fixed-width
   "C-c C-f C-t" #'rcirc-format-fixed-width ;as in AucTeX
   "C-c C-f C-d" #'rcirc-unformat
@@ -1807,7 +1807,7 @@ extracted."
   "C-c C-f C-b" #'rcirc-format-bold
   "C-c C-f C-i" #'rcirc-format-italic
   "C-c C-f C-u" #'rcirc-format-underline
-  "C-c C-f C-s" #'rcirc-format-strike-trough
+  "C-c C-f C-s" #'rcirc-format-strike-through
   "C-c C-f C-f" #'rcirc-format-fixed-width
   "C-c C-f C-t" #'rcirc-format-fixed-width ;as in AucTeX
   "C-c C-f C-d" #'rcirc-unformat
@@ -4004,6 +4004,9 @@ PROCESS is the process object for the current connection."
                      (string-equal (downcase (car setting)) parameter))
            return (cadr setting)))
 
+(define-obsolete-function-alias 'rcirc-format-strike-trough
+  'rcirc-format-strike-through "30.1")
+
 (provide 'rcirc)
 
 ;;; rcirc.el ends here