Fix VoicemailUserEntry event headers ServerEmail and MailCommand reported values.

The AMI action VoicemailUsersList VoicemailUserEntry event headers
ServerEmail and MailCommand did not report the global values if they were
not overridden.  The VoicemailUserEntry event header ServerEmail was not
populated with the global value if the voicemail user did not override it.
The VoicemailUserEntry event header MailCommand was never populated with a
value.

* Removed unused struct ast_vm_user member mailcmd[].

(closes issue AST-973)
Reported by: John Bigelow
Tested by: rmudgett
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Merged revisions 372620 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 372621 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 372622 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@372623 65c4cc65-6c06-0410-ace0-fbb531ad65f3