Remove extra defines of AST_PBX_MAX_STACK.

Remove extra defines of AST_PBX_MAX_STACK.

* Ensure AST_PBX_MAX_STACK is only defined in extconf.h and pbx.h.
* Fix incorrect function parameters in utils/extconf.c.

(closes issue ASTERISK-23141)
Reported by: Maxim
Review: https://reviewboard.asterisk.org/r/3241/
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Merged revisions 408785 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 408786 from http://svn.asterisk.org/svn/asterisk/branches/11

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@408787 65c4cc65-6c06-0410-ace0-fbb531ad65f3