docs(adr-025): remove duplicate [login_flow] section in TOML example

Commit 4 renamed `[oauth_single_audience]` → `[login_flow]` via a global
sed pass, but ADR-025's example settings.toml already had a `[login_flow]`
section just above the `[keycloak]` block. The rename produced two
back-to-back `[login_flow]` headers with identical contents — TOML parsers
either reject the file or silently override, and a reader copying the
example would land on either outcome.

Dropped the now-duplicate second `[login_flow]` section (the renamed one).
The earlier `[login_flow]` section retains the same content + a comment
explaining the ADR-022 derivation, so no information is lost.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/ADR-025-dynaconf-configuration-management.md

@@ -211,9 +211,6 @@ token_storage_db = "/app/data/tokens.db"
 enable_token_exchange = true
 token_storage_db = "/app/data/tokens.db"
 token_exchange_cache_ttl = 300
-
-[login_flow]
-token_storage_db = "/app/data/tokens.db"
 ```
 
 **`.secrets.toml.example`** — Template, checked into git (actual `.secrets.toml` is gitignored):