amalloc has 0 callers post-γ-2; the *arena threaded through w6a's
init/dupstr/bufinit and the asm_.a / buf.a fields are vestigial.
Drop `import mem;` from opcodes/parse/obj/main, remove asm_.a and
buf.a struct fields, strip *arena from init/dupstr/bufinit
signatures, update 12 call sites. main.combined.ww auto-regenerated.
Comment at main.ww:36 retidied "argv/arena" → "argv-style" to match
post-strip reality.
Verified 132/132 incl. 991_w6a_ww + 995_self_rebuild byte-identity.
Hojun-Cho
12e0b4057f