Stop describing a base curve the pipeline no longer has

D19 retired the per-body base curve, moved the matrix ahead of the
edits and the film into the view transform's place, but a dozen doc
comments still listed the curve among what a pixel passes through, or
said the film skipped it. The detail stage's module doc still drew the
matrix after the edits and the last detail pass encoding, which the
view pass took over. The film crate's README gave the base curves as
its reason for being data, and the ops README's list of hand-written
nodes had neither the view transform nor three of the five kernels.

FR-MRG-2 gave the base curve as why the merge cuts below the profile;
the view transform is why now. The decision table still said colour
defaults were a per-body curve, and FR-DEV-3j said only the default
view transform skips a JPEG, where the node skips one whatever its
sliders say. frame-budget.md records the view pass as unmeasured.

core/dr-pipeline/ops/film_sim.yaml

@@ -11,8 +11,8 @@ why_rust: |
   characteristic curves and a density lookup — which are not parameters and
   which no `uniforms:` expression could produce. Its neutral is "no stock
   loaded" rather than a set of values, and it is the one node that declares
-  `Operation::renders`, so the composer omits the camera profile's base curve
-  and the conversion out of camera space on its behalf.
+  `Operation::renders`, so while a stock is loaded the composer emits it in
+  the view transform's place instead of the default sigmoid.
 
 placement: |
   Last, in the view transform's place (D19, FR-DEV-3j), after every other