test: re-cite retired-mechanism comments in surviving carriers

The migrate-and-retire audit left the surviving carriers as the only
files still describing the retired combined.ww amalgamator as live:
m2wwi/m3sep headers claimed .wwi was dead code, four byteid carriers
carried dead cleanup of never-written .combined.ww intermediates, and
sepbuild's enumeration mirror plus lib_byteid's completeness scan
still skipped the retired artifact form (the same silent
accommodation just removed from both drivers — dropping it here
surfaced and flushed 39 stale untracked amalgamator outputs across
lib/, which the gates now reject loudly). Remaining mentions are
past-tense history or quoted diagnostics.

test/wcc/848_xmod_qualstructlit_run.c

@@ -53,8 +53,8 @@
  * or the two stages' .s diverged (rule-10 break).
  *
  * Builds its own 2-module fixtures in a private mktemp dir, so all
- * intermediates (main.combined.ww, the linked binary, the .s probes)
- * land OFF the source tree (CLAUDE.md rule 14).
+ * intermediates (the linked binary, the .s probes) land OFF the
+ * source tree (CLAUDE.md rule 14).
  */
 #include <stdio.h>
 #include <stdlib.h>