build: restore offline-first policy (REDBEAR_RELEASE + drop vendored gnu-config)

- .config: restore REDBEAR_RELEASE?=0.1.0. The previous commit
  (f6241fb80e) dropped it, which violates the release model in
  local/AGENTS.md (sources are frozen at the 0.1.0 release and
  the .config file must declare the active release identifier
  so the build is reproducible).
- src/cook/gnu-config/{config.guess,config.sub}: remove the
  vendored copies added in the previous commit. Modifying
  src/ directly violates the policy in local/AGENTS.md:
  'DO NOT modify mk/ or src/ directly — extend via local/scripts/'.
  Any offline fallback for GNU_CONFIG_GET should live in
  local/scripts/, not in mainline src/.

Per local/AGENTS.md STUB AND WORKAROUND POLICY (zero tolerance for
stubs, workarounds, sed/awk hacks, etc.) and RELEASE MODEL (FORK —
sources frozen, REDBEAR_RELEASE required).

.config

@@ -1 +1,3 @@
 PODMAN_BUILD?=0
+
+REDBEAR_RELEASE?=0.1.0