remove mentions of the Slug header from the LWS protocol text

[ghurlbot]

Opened by @laurensdeb via IRC channel #lws on irc.w3.org

Due: 2026-08-10 (Monday 10 August)

[elf-pavlik]

resolution to

• Use of the Slug header in the LWS protocol text #94

PR should resolve and autoclose both issues