Stage I: strip dead code -- pump drain loop, SWITCH-MARK-WORK, global interpret depth, native_switch_back_to (FABRIC-3.8 §4 row I)

Each shown dead three ways (FABRIC-3.5 §XXII): the pump loop by its
condition, by construction (birth cap == switch table capacity, every birth
registers) and at run time (probe silent through boot, G interleave, an
8-worker DoE trial and the relay); SWITCH-MARK-WORK by callers, capsules
(source and baked), experiments/tools/logs; the depth counter and back_to
field by having no readers.

Kept: Hera's own pump drain (last timer-paced delivery, Hera only) and the
always-0 readiness CSV columns (a DoE schema call). Acceptance on amd64/
aarch64/riscv64: G interleave unchanged, cfg-0 trial fail=0 2/2 dead,
relay 3, idle growth 0; dict_hash set changed by the removed word
(word_count 531) and identical across ISAs. FABRIC-3.8 stages A-I done.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

include/starkernel/capsule_vm_switch_signal.h

@@ -169,10 +169,6 @@ void sk_vm_switch_reap_pending(void);
  * CSV counters below. */
 void sk_vm_switch_signal_note_switch_performed(VMUuid target_id);
 
-/* SWITCH-MARK-WORK's body. Stage C-b: no flag to set any more (the queue
- * is the eligibility); only asks for a fresh decision. */
-void sk_vm_switch_signal_mark_work(VMUuid vm_id);
-
 /* DoE CSV read-only exposure (FABRIC-3.md §XXVIII Stage 3 follow-on,
  * 2026-09-13). Stage C-b: ticks_since_switch now counts beats of the
  * running VM since the last switch (§3.13.4), not ISR ticks; the per-VM