res_smdi: convert to astobj2

Remove functions:
	ast_smdi_interface_unref
	ast_smdi_md_message_putback
	ast_smdi_mwi_message_putback
	ast_smdi_md_message destructor
	ast_smdi_mwi_message destructor

Includes for astobj.h are removed everywhere it's possible.

ASTERISK-24066 #close
Review: https://reviewboard.asterisk.org/r/3758/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@419060 f38db490-d61c-443f-a65b-d21fe96a405b