syslogd: Remove addfile() and free up some memory

[jfree]

Summary

cfline() already allocates a filed structure on the heap, so we can
avoid redundant memory allocations by skipping a second calloc() inside
addfile().

addfile() can be removed altogether since a simple STAILQ_INSERT_TAIL()
will add the filed to the global filed list.

[jfree]

Update diff with context

[jfree]

Update after rebase

[emaste]

I think it would have been a bit clearer if D41358 was first, although it's not worth extra effort to recreate the patch set that way.