Remove duplicate key definitions from keymaps

* lisp/gnus/gnus-srvr.el (gnus-browse-mode-map): Remove binding for
'gnus-browse-prev-map'.
* lisp/gnus/gnus-sum.el (gnus-summary-mode-map): Remove
'gnus-summary-down-thread' binding, and by symmetry
'gnus-summary-up-thread' (it's still available on "T-u").
* lisp/ibuffer.el (ibuffer-mode-map): Remove binding for
'ibuffer-mark-for-delete'.
* lisp/wdired.el (wdired-perm-mode-map): Remove duplicate binding of
"s" to 'wdired-set-bit'.

* etc/NEWS: Announce 'gnus-summary-up-thread' change.

etc/NEWS

@@ -1644,6 +1644,12 @@ Message, referred to as 'gnus-summary-tool-bar-retro',
 well as the icons used), and the "Gnome" tool bars are now the only
 pre-defined toolbars.
 
+---
+*** 'gnus-summary-up-thread' and 'gnus-summary-down-thread' bindings removed.
+The 'gnus-summary-down-thread' binding to "M-C-d" was shadowed by
+'gnus-summary-read-document', and these commands are also available on
+"T-u" and "T-d" respectively.
+
 ---
 *** Gnus now uses a variable-pitch font in the headers by default.
 To get the monospace font back, you can put something like the

lisp/gnus/gnus-srvr.el

@@ -699,7 +699,6 @@ claim them."
   "n" #'gnus-browse-next-group
   "p" #'gnus-browse-prev-group
   "DEL" #'gnus-browse-prev-group
-  "<delete>" #'gnus-browse-prev-group
   "N" #'gnus-browse-next-group
   "P" #'gnus-browse-prev-group
   "M-n" #'gnus-browse-next-group

lisp/gnus/gnus-sum.el

@@ -1958,8 +1958,6 @@ increase the score of each group you read."
   "C-M-b" #'gnus-summary-prev-thread
   "M-<down>" #'gnus-summary-next-thread
   "M-<up>" #'gnus-summary-prev-thread
-  "C-M-u" #'gnus-summary-up-thread
-  "C-M-d" #'gnus-summary-down-thread
   "&" #'gnus-summary-execute-command
   "c" #'gnus-summary-catchup-and-exit
   "C-w" #'gnus-summary-mark-region-as-read

lisp/ibuffer.el

@@ -447,7 +447,6 @@ directory, like `default-directory'."
 
   "d"           #'ibuffer-mark-for-delete
   "C-d"         #'ibuffer-mark-for-delete-backwards
-  "k"           #'ibuffer-mark-for-delete
   "x"           #'ibuffer-do-kill-on-deletion-marks
 
   ;; immediate operations

lisp/wdired.el

@@ -902,7 +902,6 @@ Like original function but it skips read-only words."
   "x"   #'wdired-set-bit
   "-"   #'wdired-set-bit
   "S"   #'wdired-set-bit
-  "s"   #'wdired-set-bit
   "T"   #'wdired-set-bit
   "t"   #'wdired-set-bit
   "s"   #'wdired-set-bit