conf: removed the deprecated "error_file" option

This option was deprecated by the 0.15 release.  This patch makes this
option invalid.

NEWS

@@ -22,6 +22,7 @@ ver 0.16 (20??/??/??)
 * commands:
   - added new "status" line with more precise "elapsed time"
 * log unused/unknown block parameters
+* removed the deprecated "error_file" option
 * save state when stopped
 * renamed option "--stdout" to "--stderr"
 * obey $(sysconfdir) for default mpd.conf location

src/conf.c

@@ -53,7 +53,6 @@ static struct config_entry config_entries[] = {
 	{ .name = CONF_DB_FILE, false, false },
 	{ .name = CONF_STICKER_FILE, false, false },
 	{ .name = CONF_LOG_FILE, false, false },
-	{ .name = CONF_ERROR_FILE, false, false },
 	{ .name = CONF_PID_FILE, false, false },
 	{ .name = CONF_STATE_FILE, false, false },
 	{ .name = CONF_USER, false, false },

src/conf.h

@@ -30,7 +30,6 @@
 #define CONF_DB_FILE                    "db_file"
 #define CONF_STICKER_FILE "sticker_file"
 #define CONF_LOG_FILE                   "log_file"
-#define CONF_ERROR_FILE                 "error_file"
 #define CONF_PID_FILE                   "pid_file"
 #define CONF_STATE_FILE                 "state_file"
 #define CONF_USER                       "user"