Deprecation of legacy ss:// link format

SIP002 has been the standard of ss:// URL scheme for over 3 years. During the period, almost all Shadowsocks clients have added support for SIP002 URLs. Many implementations now actually default to SIP002 URLs when exporting as links. This includes Outline server and Qv2ray. Some new implementations like shadowsocks-rust only support SIP002 URLs.

Shadowsocks-windows has been using SIP002 as the default ss:// URL scheme since v4.2.0. Support for the legacy ss:// link format has effectively been dropped in v5 by the reimplementation of the URL parser and generator.

We are looking to get other implementations to work together with us to deprecate the legacy link format, and towards the ultimate goal of completely dropping support for it.

To begin with, I'm proposing that all client implementations should remove the ability to export links in the legacy link format. Our website should be updated to reflect the deprecation status.

Related issue: #152.

Read related issue #152, then inspect the website content that describes ss:// links and current compatibility. The requested result is updated website wording that reflects legacy-format deprecation; the broader client-implementation coordination is outside this repository's stated scope.