Stop naming a specific commercial disc in the label parser

Two comments identified the disc the STN-numbering bug was found on by its
vendor project name. The reproduction does not need it: what matters is the
SHAPE of the token list — placeholder slots, region-only tokens, an
uncatalogued component — not which release happened to exhibit it. Both now
describe the shape.

The remaining `SEG_MainFeature` references stay. That is a vendor section name
the parser matches on at pixelogic.rs:88, not a disc identifier — it is the
format's vocabulary, like `FPL_` or the `eng_MLP_` stream tokens beside it, and
removing it would break the parser.

Also drops the last prohibited citation from the changelog: an mp4:// bullet
said "no ffmpeg". The website changelog page is REGENERATED from this file at
release time, so a scrub of the site alone would have been reverted by the next
release.

CHANGELOG.md

@@ -335,7 +335,7 @@
   any sink (`mp4:// mkv://`, `mp4:// audio://`, `mp4:// json://`, …). The round-trip
   is frame-exact.
 - **Native MP4 output (`mp4://`)** — a disc goes straight to a play-everywhere
-  `.mp4` in one decrypt pass, no ffmpeg. Carries HEVC / H.264 video (with HDR10) and
+  `.mp4` in one decrypt pass, no external transcoder. Carries HEVC / H.264 video (with HDR10) and
   AC-3, E-AC-3, and DTS / DTS-HD audio, and is faststart by default so it plays over
   HTTP without downloading the end first. It's a **compatibility export, not
   archival**: MP4 can't hold TrueHD, LPCM, or bitmap (PGS / VobSub) subtitles, so