clang compiler warnings: Fix a variety of "unused" warnings

This patch fixes the -Wunused-value -Wunused-variable -Wunused-const-variable
errors caught by clang. Specifically:

* apps/app_queue.c: removed unused qpm_cmd_usage[], qum_cmd_usage[],
                    qsmp_cmd_usage[]
* cel/cel_sqlite3_custom.c: removed unused name[] = "cel_sqlite3_custom"
* channels/chan_pjsip.c: removed unused desc[] = "PJSIP Channel"
* codecs/gsm/src/gsm_create.c: removed unused ident[] = "$Header$"
* funcs/func_env.c:729: Fixed ast_str_append_substr.
* main/editline/np/strlcat.c: removed unused rcsid variable
* main/editline/np/strlcpy.c: removed unused rcsid variable
* main/security_events.c: removed unused TIMESTAMP_STR_LEN
* utils/conf2ael.c: removed unused cfextension_states
* utils/extconf.c: removed unused cfextension_states

Review: https://reviewboard.asterisk.org/r/4526

ASTERISK-24917
Reported by: dkdegroot
patches:
  rb4526.patch submitted by dkdegroot (License 6600)
........

Merged revisions 433693 from http://svn.asterisk.org/svn/asterisk/branches/11
........

Merged revisions 433694 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@433695 65c4cc65-6c06-0410-ace0-fbb531ad65f3

codecs/gsm/src/gsm_create.c

@@ -4,8 +4,6 @@
  * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
  */
 
-static char const	ident[] = "$Header$";
-
 #include	"config.h"
 
 #ifdef	HAS_STRING_H