Removal of sccp_channel_set_line. Channel->line should be read-only and constant (We might actually have to change the definition in chan_sccp.h to be const to make absolutely sure).

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5333 43c1dc8c-776e-4df2-8ef1-6e829299be21