Remove POSIX 'cpoptions': '&'

runtime/doc/options.txt

@@ -1946,10 +1946,6 @@ A jump table for the options with a short description can be found at |Q_op|.
 	when $VIM_POSIX was set on startup. |posix|
 
 	    contains	behavior	~
-								*cpo-&*
-		&	When ":preserve" was used keep the swap file when
-			exiting normally while this buffer is still loaded.
-			This flag is tested when exiting.
 								*cpo-\*
 		\	Backslash in a [] range in a search pattern is taken
 			literally, only "\]" is special  See |/[]|

runtime/doc/recover.txt

@@ -111,10 +111,6 @@ command:
 					*:pre* *:preserve* *E313* *E314*
 :pre[serve]		Write all text for all buffers into swap file.  The
 			original file is no longer needed for recovery.
-			This sets a flag in the current buffer.  When the '&'
-			flag is present in 'cpoptions' the swap file will not
-			be deleted for this buffer when Vim exits and the
-			buffer is still loaded |cpo-&|.
 
 A Vim swap file can be recognized by the first six characters: "b0VIM ".
 After that comes the version number, e.g., "3.0".

src/nvim/memline.c

@@ -587,8 +587,7 @@ void ml_close(buf_T *buf, int del_file)
 void ml_close_all(int del_file)
 {
   FOR_ALL_BUFFERS(buf) {
-    ml_close(buf, del_file && ((buf->b_flags & BF_PRESERVED) == 0
-                               || vim_strchr(p_cpo, CPO_PRESERVE) == NULL));
+    ml_close(buf, del_file && ((buf->b_flags & BF_PRESERVED) == 0));
   }
   spell_delete_wordlist();      /* delete the internal wordlist */
   vim_deltempdir();             /* delete created temp directory */

src/nvim/option_defs.h

@@ -129,7 +129,6 @@
 #define CPO_SPECI       '<'     /* don't recognize <> in mappings */
 #define CPO_REGAPPEND   '>'     /* insert NL when appending to a register */
 /* POSIX flags */
-#define CPO_PRESERVE    '&'     /* keep swap file after :preserve */
 #define CPO_SUBPERCENT  '/'     /* % in :s string uses previous one */
 #define CPO_BACKSL      '\\'    /* \ is not special in [] */
 #define CPO_CHDIR       '.'     /* don't chdir if buffer is modified */
@@ -139,7 +138,7 @@
 #define CPO_VIM         "aABceFs"
 #define CPO_VI          "aAbBcCdDeEfFiIJkKlLmMnoOpPqrRsStuvWxXyZ$!%+<>;"
 #define CPO_ALL \
-  "aAbBcCdDeEfFiIJkKlLmMnoOpPqrRsStuvWxXyZ$!%+<>&/\\.;"
+  "aAbBcCdDeEfFiIJkKlLmMnoOpPqrRsStuvWxXyZ$!%+<>/\\.;"
 
 /* characters for p_ww option: */
 #define WW_ALL          "bshl<>[],~"