toolchain: banner purge + WHY-only comment sweep (rule 8)

selfhost/, cmd/, internal/ join the tree-wide sweep: every section
banner dies (91 selfhost + the cmd C-style dividers -> 0); narration
and stale contracts deleted (pre-#22 bundler notes, retired
single-PT_LOAD and no-archive claims, superseded ABI tables); every
ref/harec/qbe cite, task cite, encoding/ELF contract, and rule-10
twin pointer kept; lost lifetime/rationale lines restored where the
sweep over-cut (elf_globals ownership, kwtab linear-scan). Comment-
only proven: all five wwstage tool binaries byte-identical across
the sweep; test-commit, test-byteid (161+1399, 0 pinned-divergent),
and test-bootstrap (fixed point + 991-995 byte-id) all exit 0.
The read-through banked 66 latent-bug leads (checkpoint).

cmd/w6a/a.h

@@ -1,10 +1,7 @@
 /*
- * a.h — w6a-private header. Modelled on Plan 9 cmd/6a/a.h, trimmed
- * to the instruction subset that w6c emits.
- *
- * w6a is line-oriented and has no preprocessor: each non-blank, non-
- * label line is one instruction. We read the whole file into a list
- * of `Aprog`s, then encode and emit ELF64.
+ * Modelled on Plan 9 cmd/6a/a.h, trimmed to the instruction subset
+ * that w6c emits. Line-oriented, no preprocessor: each non-blank,
+ * non-label line is one instruction.
  */
 #ifndef SIX_A_H
 #define SIX_A_H
@@ -69,17 +66,14 @@ struct Areloc {
 };
 
 struct Asm {
-	/* parser state */
 	const char *file;
 	const char *src;
 	u64	srclen;
 	u64	pos;
 	int	line;
 
-	/* program list */
 	Aprog	*head, *tail;
 
-	/* output text section */
 	u8	*text;
 	u64	textcap, textlen;
 
@@ -89,7 +83,6 @@ struct Asm {
 	u8	*data;
 	u64	datacap, datalen;
 
-	/* symbols */
 	Asym	*syms;
 	Areloc	*relocs;