End-of-life declaration of NetBSD 1.4 branch

In keeping with NetBSD's policy of maintaining only the current and
most recent release, the releast of NetBSD 1.6 marks the end-of-life
for NetBSD 1.4.  This means that the netbsd-1-4 branch will no longer be
maintained.

For example:

- There will be no pullups made (even for security issues)
- There will be no security advisories made for 1.4

itojun
on behalf of core@netbsd.org