The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The new implementation is copied from another project and is
BSD-licensed.  It is exception-safe and can parse IPv6 scope ids with
interface names.

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Fixes build failure because Bionic doesn't provide SUN_LEN().