lib: move \n vs. \r\n handling into vty code

lib: move \n vs. \r\n handling into vty code

Instead of having an ?: expression embedded in every single caller of
vty_out, just expand \n to \r\n in the vty code if neccessary.

(Deprecation warnings will be enabled in the next commits which will do
the search-and-replace over the codebase.)

[This reverts commit 4d5f445 "lib: add vty_outln()"]

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>