Call the reference curve what it is, and drop wording that reads as copying

The view transform's second curve is the DNG SDK's published reference
rendering — the ACR3 default curve applied by RefBaselineRGBTone — so
it is the "DNG Reference" curve in the panel, D21 and the code, not a
name borrowed from another product. Comments and docs that justified a
choice by another editor doing it ("as their Amount", "so a
photographer arriving from it finds the name") now give the actual
reason. The Vivid presets no longer describe themselves as reaching
for another editor's look; they are DarkRoom's own.

Factual mentions stay: which program wrote the library's DNGs, what
was measured against, and preset import. camera-profiles.md gains §15,
on starting a photograph from the edit it already carries.

core/dr-gpu/tests/view_transform.rs

@@ -61,7 +61,7 @@ fn sigmoid_chain() -> EditGraph {
 #[test]
 fn camera_raw_tone_agrees_with_the_acr3_curve() {
     // TRACES: FR-DEV-3j
-    // D21: a raw with no profile, Camera Raw's curve chosen, renders a grey
+    // D21: a raw with no profile, the DNG reference curve chosen, renders a grey
     // through the ACR3 default curve, which the profile buffer's placeholder
     // carries.
     let Some(ctx) = ctx() else {