Clarify the deprecation notice about Macro() to note that it will not be removed

for the sake of backwards compatibility, since it is a non-trivial task to convert
existing large dialplans that depend on Macro() to use GoSub(), instead.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@114931 65c4cc65-6c06-0410-ace0-fbb531ad65f3