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/
........

Merged revisions 408785 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@408786 65c4cc65-6c06-0410-ace0-fbb531ad65f3