MEDIUM: config: remove the deprecated and dangerous global "debug" directive

This one was scheduled for removal in 2.3 since 2.2-dev3 by commit
1b85785bc ("MINOR: config: mark global.debug as deprecated"). Let's
remove it now. It remains totally possible to use -d on the command
line though.

doc/configuration.txt

@@ -717,7 +717,6 @@ The following keywords are supported in the "global" section :
    - tune.zlib.windowsize
 
  * Debugging
-   - debug
    - quiet
    - zero-warning
 
@@ -2317,12 +2316,6 @@ tune.zlib.windowsize <number>
 3.3. Debugging
 --------------
 
-debug (deprecated)
-  Enables debug mode which dumps to stdout all exchanges, and disables forking
-  into background. It is the equivalent of the command-line argument "-d". It
-  should never be used in a production configuration since it may prevent full
-  system startup.
-
 quiet
   Do not display any message during startup. It is equivalent to the command-
   line argument "-q".

doc/management.txt

@@ -196,9 +196,8 @@ list of options is :
     error is encountered. Presence of warnings will be reported if any.
 
   -d : enable debug mode. This disables daemon mode, forces the process to stay
-    in foreground and to show incoming and outgoing events. It is equivalent to
-    the "global" section's "debug" keyword. It must never be used in an init
-    script.
+    in foreground and to show incoming and outgoing events. It must never be
+    used in an init script.
 
   -dG : disable use of getaddrinfo() to resolve host names into addresses. It
     can be used when suspecting that getaddrinfo() doesn't work as expected.

src/cfgparse-global.c

@@ -58,14 +58,6 @@ int cfg_parse_global(const char *file, int linenum, char **args, int kwm)
 		}
 		global.mode |= MODE_MWORKER;
 	}
-	else if (!strcmp(args[0], "debug")) {
-		if (alertif_too_many_args(0, file, linenum, args, &err_code))
-			goto out;
-		global.mode |= MODE_DEBUG;
-		ha_warning("parsing [%s:%d] : '%s' must never be used and will be removed in 2.3. If you need debug mode, please use '-d' on the command line.\n", file, linenum, args[0]);
-		err_code |= ERR_WARN;
-		goto out;
-	}
 	else if (!strcmp(args[0], "noepoll")) {
 		if (alertif_too_many_args(0, file, linenum, args, &err_code))
 			goto out;

tests/test-fsm.cfg

@@ -256,7 +256,6 @@
 global
 	maxconn 100
 	log		127.0.0.1 local0
-	debug
 
 # connect to port 8000 to consult statistics
 listen stats