docs: drop the last "a build that adds sm_120" phrasing

Audit leftover in the same file: the "Keeping the change" note explained that
the default pin cannot move because "a build that adds sm_120 can drop older
architectures". That still implies the pinned build lacks sm_120, sixty lines
below the corrected cause. The reason the default cannot move is simply that a
newer build can drop older GPUs, which cu128 already did for Maxwell and
Pascal.

Deliberately not restating the resulting floor. docs/competitive-analysis.md
says Turing sm_75, but the pinned 2.8.0+cu128 build reports sm_70 first, so the
claim is unverified and left out rather than copied.

Signed-off-by: Moep90 <volleyballlive@googlemail.com>

Signed-off-by: moep90 <volleyballlive@googlemail.com>

docs/install/troubleshooting.md

@@ -317,8 +317,8 @@ guarded now, so the upgrade path above is clean on a current checkout.
 **Keeping the change:** these are the repo's own pins, so a `git pull` that
 touches them will conflict or overwrite. Re-apply after updating until the
 default pin moves — the default cannot move for everyone until the newer torch
-is verified across the older GPUs VoiceStudio supports, since a build that adds
-`sm_120` can drop older architectures.
+is verified across the older GPUs VoiceStudio supports, since a newer build can
+drop older architectures — the cu128 wheels already dropped Maxwell and Pascal.
 
 **Linked issue:** [#1931](https://github.com/debpalash/VoiceStudio/issues/1931)
 — thanks to the reporter for the full diagnosis, including the verification