Remove v1.8.17 packages (GHSA-55f2-h36g-96c3) (#8)

v1.8.17 is affected by GHSA-55f2-h36g-96c3: PasswordToken, EmailToken
and RegistrationToken use `token` as a string primary key but never
declared `$keyType = 'string'`, so Eloquent defaulted to `int` and a
request supplying a bare integer `0` matched any token MySQL coerces to
`0` — enabling password-reset account takeover.

v1.8.19 is the only non-vulnerable 1.x release, and its packages are
already published in packages/v1.x/v1.8.19/. The 1.x docs download table
was regenerated by the v1.8.19 build and no longer links to v1.8.17, so
these files are unreferenced.

Author: imorland