Remove old 5.1-* bits

[Makoto Matsushita]

matusita> And, how about 4.6.2-RELEASE for i386/alpha?  We have removed all
matusita> packages for 4.6.2 already.

Oops, s/alpha//; (i.e. packages-4.6.2-release is there for alpha).
Speaking about alpha, there's still 4.4-RELEASE which packages were no
longer there.

Yet another "removing them all" candidate will be in
releases/${arch}/ISO-IMAGES directory.

-- -
Makoto `MAR' Matsushita