Fix -Werror=unused-but-set-variable compile error in utils/extconf.c.

Note that I'm not confirming legitimacy of having that file in tree at
all. Is anyone using aelparse/conf2ael?

(issue ASTERISK-15350)
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Merged revisions 350885 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 350886 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@350887 65c4cc65-6c06-0410-ace0-fbb531ad65f3