Remove the layout undo/redo code which never really worked.

tmux.1

@@ -1601,7 +1601,7 @@ lower) with
 .Fl U
 or downward (numerically higher).
 .It Xo Ic select-layout
-.Op Fl npUu
+.Op Fl np
 .Op Fl t Ar target-window
 .Op Ar layout-name
 .Xc
@@ -1618,13 +1618,6 @@ are equivalent to the
 and
 .Ic previous-layout
 commands.
-.Pp
-.Fl U
-and
-.Fl u
-step forward and back through previous layouts, up to the maximum set by the
-.Ic layout-history-limit
-option.
 .It Xo Ic select-pane
 .Op Fl lDLRU
 .Op Fl t Ar target-pane
@@ -2677,13 +2670,6 @@ or
 .Ar height .
 A value of zero restores the default unlimited setting.
 .Pp
-.It Ic layout-history-limit Ar limit
-Set the number of previous layouts stored for recovery with
-.Ic select-layout
-.Fl U
-and
-.Fl u .
-.Pp
 .It Ic main-pane-height Ar height
 .It Ic main-pane-width Ar width
 Set the width or height of the main (left or top) pane in the