sounds: Fix Sounds Makefile and XML that didn't support new sound prompt sets

In sounds/Makefile

 1 Adds and moves some lines necessary for the en_GB core set. I'm just following how the other sets are defined here.
 2 removes the ES extra sounds related lines as we don't have ES extra sound sets. 

In sounds/sounds.xml

 3 Adds member definitons for EN_AU, EN_GB, IT for core sound sets, and EN_GB in extra sound sets

ASTERISK-23550 #close
Review: https://reviewboard.asterisk.org/r/3464/
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Merged revisions 412586 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@412587 f38db490-d61c-443f-a65b-d21fe96a405b