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single-PT_LOAD and no-archive claims, superseded ABI tables); every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).

selfhost/cmd/w6c/main.ww

@@ -1,14 +1,4 @@
-// selfhost/cmd/w6c/main.ww — port of cmd/w6c/main.c.
-//
-// w6c = amd64 compiler. Read .ww, parse, codegen, emit Plan 9 amd64
-// asm to stdout (or the file given by -o).
-//
-//   w6c_ww -o file.s file.ww
-//
-// The cgen routines in selfhost/cmd/wcc/cgen.ww write directly to
-// fd 1 via os.write(1, ...). For -o, we open the output file and
-// dup2 it onto fd 1 before invoking cgfile. This is the same trick
-// the bootstrap uses with shell redirection, just in-process.
+// Port of cmd/w6c/main.c.
 
 package main;