app_speech_utils: Fix unresolved symbol ast_speech_get_setting().

Fixes regression introduced by -r374096.

* Made res_speech.export.in export ast_* symbols instead of specific
functions.

* Made app_speech_utils.c declare that it is dependent upon res_speech.

(issue ASTERISK-17136)
Reported by: Richard Kenner
........

Merged revisions 399197 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399198 65c4cc65-6c06-0410-ace0-fbb531ad65f3