options: Remove 'esckeys' (#6138)

This was never supported and it does not make sense for Nvim.

runtime/doc/insert.txt

@@ -370,9 +370,6 @@ CTRL-G U	don't break undo with next left/right cursor *i_CTRL-G_U*
 		within same the line)
 -----------------------------------------------------------------------
 
-Note: If the cursor keys take you out of Insert mode, check the 'noesckeys'
-option.
-
 The CTRL-O command sometimes has a side effect: If the cursor was beyond the
 end of the line, it will be put on the last character in the line.  In
 mappings it's often better to use <Esc> (first put an "x" in the text, <Esc>

runtime/doc/options.txt

@@ -2209,18 +2209,6 @@ A jump table for the options with a short description can be found at |Q_op|.
 	Scanf-like description of the format for the lines in the error file
 	(see |errorformat|).
 
-				     *'esckeys'* *'ek'* *'noesckeys'* *'noek'*
-'esckeys' 'ek'		boolean	(Vim default: on, Vi default: off)
-			global
-	Function keys that start with an <Esc> are recognized in Insert
-	mode.  When this option is off, the cursor and function keys cannot be
-	used in Insert mode if they start with an <Esc>.  The advantage of
-	this is that the single <Esc> is recognized immediately, instead of
-	after one second.  Instead of resetting this option, you might want to
-	try changing the values for 'timeoutlen' and 'ttimeoutlen'.  Note that
-	when 'esckeys' is off, you can still map anything, but the cursor keys
-	won't work by default.
-
 						*'eventignore'* *'ei'*
 'eventignore' 'ei'	string	(default "")
 			global

runtime/doc/quickref.txt

@@ -678,7 +678,6 @@ Short explanation of each option:		*option-list*
 'errorbells'	  'eb'	    ring the bell for error messages
 'errorfile'	  'ef'	    name of the errorfile for the QuickFix mode
 'errorformat'	  'efm'     description of the lines in the error file
-'esckeys'	  'ek'	    recognize function keys in Insert mode
 'eventignore'	  'ei'	    autocommand events that are ignored
 'expandtab'	  'et'	    use spaces when <Tab> is inserted
 'exrc'		  'ex'	    read .nvimrc and .exrc in the current directory

runtime/doc/term.txt

@@ -70,9 +70,7 @@ for a next character to arrive.  If it does not arrive within one second a
 single <Esc> is assumed.  On very slow systems this may fail, causing cursor
 keys not to work sometimes.  If you discover this problem reset the 'timeout'
 option.  Vim will wait for the next character to arrive after an <Esc>.  If
-you want to enter a single <Esc> you must type it twice.  Resetting the
-'esckeys' option avoids this problem in Insert mode, but you lose the
-possibility to use cursor and function keys in Insert mode.
+you want to enter a single <Esc> you must type it twice.
 
 Some terminals have confusing codes for the cursor keys.  The televideo 925 is
 such a terminal.  It sends a CTRL-H for cursor-left.  This would make it

runtime/doc/vim_diff.txt

@@ -298,6 +298,7 @@ Other options:
   'antialias'
   'cpoptions' ("g", "w", "H", "*", "-", "j", and all POSIX flags were removed)
   'encoding' ("utf-8" is always used)
+  'esckeys'
   'guioptions' "t" flag was removed
   *'guipty'* (Nvim uses pipes and PTYs consistently on all platforms.)
   *'imactivatefunc'* *'imaf'*

runtime/optwin.vim

@@ -524,8 +524,6 @@ endif
 
 
 call <SID>Header("terminal")
-call append("$", "esckeys\trecognize keys that start with <Esc> in Insert mode")
-call <SID>BinOptionG("ek", &ek)
 call append("$", "scrolljump\tminimal number of lines to scroll at a time")
 call append("$", " \tset sj=" . &sj)
 if has("gui") || has("msdos") || has("win32")