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"
* 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
* 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)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@433693 65c4cc65-6c06-0410-ace0-fbb531ad65f3