docs: remove NIP-FI migration gate from release procedure (#8567)

The NIP-FI migration prerequisite currently makes every desktop, CLI,
and mobile release reverify all supported relay deployments. Remove that
section from `RELEASING.md` once the supported relay fleet has completed
the migration, so routine client releases no longer stop on this
historical prerequisite.

This draft does not establish that the migration is complete.
Confirmation from the relay owner is still pending.

### Before merge

- [ ] Confirm that no supported relay deployment still needs the
post-transfer upload-expiry fix described in the [existing release
prerequisite](https://github.com/block/buzz/blob/mobile-v0.26.0-rc.1/RELEASING.md#nip-fi-upload-proof-freshness-relay-floor).

### Validation

Documentation-only deletion. Checked the diff and searched repository
Markdown for references to the removed section; no other Markdown
references were found. No runtime behavior changes.

Signed-off-by: Tom Brow <tomb@block.xyz>
Co-authored-by: tom’s astra <71920717b91a3cd951ca56cda7bee35b5d326218d81178cc16093abc1fff741b@sprout-oss.stage.blox.sqprod.co>

RELEASING.md

@@ -91,45 +91,6 @@ prior release's recorded squash commit; tag ancestry is deliberately irrelevant.
 Every push to `main` continues to publish the rolling relay `:main` and
 `:sha-<7>` tags, plus matching `:debug-main` and `:debug-sha-<7>` variants.
 
-#### NIP-FI upload proof freshness (relay floor)
-
-Desktop, CLI, and mobile clients mint Blossom upload authorization proofs with
-a **60-second expiry** (`expiration = now + 60`). **Older** relays (≤ `v0.2.1`)
-re-run the full auth verifier — including the expiry check — after receiving the
-full upload body, so a 60-second proof that was valid when admitted can expire
-during a large or slow transfer, causing a spurious rejection.
-
-The repair (commit `75e9bef748d2149ce459b14da842e706a51a5f78`, landed in this
-PR) replaces the post-body full-verifier call with a hash-only check
-(`verify_upload_hash_only`): the relay verifies the freshness and all other
-proof fields before reading the body; the only check after transfer is that the
-body's SHA-256 matches what was declared in the signed proof.
-
-Clients cannot lengthen proofs beyond 60 seconds (NIP-FI §Strict limits the
-max proof window to 60 s). This is a relay-side concern:
-
-- **The relay release that includes this PR's changes** (the first relay
-  tag > `v0.2.1`, containing commit `75e9bef748d2149ce459b14da842e706a51a5f78`)
-  performs a hash-only post-body check, eliminating the expiry window during
-  transfer. **Update this line with the concrete relay tag once it is cut.**
-- **Older self-hosted relays** (≤ `v0.2.1`) re-verify the full proof expiry
-  after transfer and may reject large uploads over slow connections.
-  Upgrading the relay is the fix; no client workaround exists within Strict
-  constraints.
-
-**Prerequisite before distributing desktop, CLI, or mobile builds that mint
-60-second upload proofs:** verify that all supported relay environments have
-been upgraded to a relay release containing commit
-`75e9bef748d2149ce459b14da842e706a51a5f78`. An unknown or unverified deployment
-does not satisfy this prerequisite. Deployments running ≤ `v0.2.1` must be
-upgraded before receiving these clients.
-
-When releasing a new **relay** version that carries the post-body hash-only
-check, record the concrete tag here so release operators can verify the
-prerequisite. When releasing **desktop, CLI, or mobile** for environments where
-self-hosted relays may be running pre-floor versions, document the floor in
-release notes and require operators to upgrade before distributing these clients.
-
 ### Mobile
 
 1. **Publish a candidate.** From a clean checkout whose `origin` is the