'cpoptions': remove "k" flag

This was already removed in 3baba1e7bc, except the documentation and
CPO_VI entry. find_term_bykeys() is irrelevant to Nvim.

runtime/doc/map.txt

@@ -444,8 +444,7 @@ There are two ways to map a special key:
    starts with <Esc>.  To enter a mapping like this you type ":map " and then
    you have to type CTRL-V before hitting the function key.  Note that when
    the key code for the key is in the |terminfo| entry, it will automatically
-   be translated into the internal code and become the second way of mapping
+   be translated into the internal code and become the second way of mapping.
-   (unless the 'k' flag is included in 'cpoptions').
 2. The second method is to use the internal code for the function key.  To
    enter such a mapping type CTRL-K and then hit the function key, or use
    the form "#1", "#2", .. "#9", "#0", "<Up>", "<S-Down>", "<S-F7>", etc.

runtime/doc/options.txt

@@ -1618,15 +1618,6 @@ A jump table for the options with a short description can be found at |Q_op|.
 		J	A |sentence| has to be followed by two spaces after
 			the '.', '!' or '?'.  A <Tab> is not recognized as
 			white space.
-								*cpo-k*
-		k	Disable the recognition of raw key codes in
-			mappings, abbreviations, and the "to" part of menu
-			commands.  For example, if <Key> sends ^[OA (where ^[
-			is <Esc>), the command ":map X ^[OA" results in X
-			being mapped to:
-				'k' included:	"^[OA"	 (3 characters)
-				'k' excluded:	"<Key>"  (one key code)
-			Also see the '<' flag below.
 								*cpo-K*
 		K	Don't wait for a key code to complete when it is
 			halfway through a mapping.  This breaks mapping

runtime/doc/vim_diff.txt

@@ -332,7 +332,7 @@ Test functions:
 
 Other options:
   'antialias'
-  'cpoptions' ("g", "w", "H", "*", "-", "j", and all POSIX flags were removed)
+  'cpoptions' (g j k H w * - and all POSIX flags were removed)
   'encoding' ("utf-8" is always used)
   'esckeys'
   'guioptions' "t" flag was removed

src/nvim/api/vim.c

@@ -153,7 +153,6 @@ String nvim_replace_termcodes(String str, Boolean from_part, Boolean do_lt,
   char *ptr = NULL;
   // Set 'cpoptions' the way we want it.
   //    FLAG_CPO_BSLASH  set - backslashes are *not* treated specially
-  //    FLAG_CPO_KEYCODE set - keycodes are *not* reverse-engineered
   //    FLAG_CPO_SPECI unset - <Key> sequences *are* interpreted
   //  The third from end parameter of replace_termcodes() is true so that the
   //  <lt> sequence is recognised - needed for a real backslash.

src/nvim/option_defs.h

@@ -97,7 +97,6 @@
 #define CPO_INTMOD      'i'     /* interrupt a read makes buffer modified */
 #define CPO_INDENT      'I'     /* remove auto-indent more often */
 #define CPO_ENDOFSENT   'J'     /* need two spaces to detect end of sentence */
-#define CPO_KEYCODE     'k'     /* don't recognize raw key code in mappings */
 #define CPO_KOFFSET     'K'     /* don't wait for key code in mappings */
 #define CPO_LITERAL     'l'     /* take char after backslash in [] literal */
 #define CPO_LISTWM      'L'     /* 'list' changes wrapmargin */
@@ -132,7 +131,7 @@
 #define CPO_CHANGEW     '_'     // "cw" special-case
 // default values for Vim and Vi
 #define CPO_VIM         "aABceFs_"
-#define CPO_VI          "aAbBcCdDeEfFiIJkKlLmMnoOpPqrRsStuvWxXyZ$!%+<>;_"
+#define CPO_VI          "aAbBcCdDeEfFiIJKlLmMnoOpPqrRsStuvWxXyZ$!%+<>;_"
 
 /* characters for p_ww option: */
 #define WW_ALL          "bshl<>[],~"