Remove Block Broadcast Fallback config

Companion to KamadoPool's df5e65d. The fallback submitter has been
scrapped — primary bitcoind remains the sole submission target, with
upstream's indefinite-retry behavior preserved. Drops the
block-broadcast-fallback union from advanced config and the
BACKUP_RPC_URLS / PENDING_BLOCKS_DIR / PENDING_BLOCKS_GRACE exports
from docker_entrypoint.

scripts/procedures/getConfig.ts

@@ -213,48 +213,6 @@ export const getConfig: T.ExpectedExports.getConfig = compat.getConfig({
           },
         },
       },
-      "block-broadcast-fallback": {
-        "type": "object",
-        "name": "Block Broadcast Fallback",
-        "description":
-          "Safety net for the moment a share meets network difficulty. ckpool always submits the block to its primary bitcoind first; if that fails (bitcoind crashed, RPC saturated, peering broken), kamado-api re-broadcasts the raw block to one or more backup RPC URLs you list here. A block is only re-submitted if it hasn't been accepted within the grace window — well-behaved primaries are never disturbed.",
-        "spec": {
-          "enabled": {
-            "type": "boolean",
-            "name": "Enable fallback broadcaster",
-            "description":
-              "Off by default. Turning on requires at least one Backup RPC URL — without one we'd just log warnings about pending blocks we can't help with.",
-            "default": false,
-          },
-          "grace-seconds": {
-            "type": "number",
-            "name": "Grace period (seconds)",
-            "description":
-              "How long a block waits before kamado-api considers ckpool's submission attempt failed and broadcasts via fallback. The patched ckpool returns from submit within ~3s rather than spinning indefinitely on a dead primary, so 3s is the right default — fast enough that fallback work happens while the block is still novel, long enough that a slow round-trip on a healthy primary doesn't trigger a spurious fallback.",
-            "nullable": false,
-            "range": "[1,600]",
-            "integral": true,
-            "units": "seconds",
-            "default": 3,
-          },
-          "backup-rpcs": {
-            "type": "list",
-            "name": "Backup Bitcoin RPC URLs",
-            "description":
-              "Each entry is a full bitcoind RPC URL, optionally with credentials inline (https://user:pass@host:8332/). Used in order. Anything that speaks the standard JSON-RPC submitblock method works — a second self-hosted bitcoind, an authenticated public RPC service (Quicknode, GetBlock.io, Allnodes, etc.), or a peer node you trust. Leaving this empty disables the broadcaster.",
-            "subtype": "string",
-            "spec": {
-              "pattern": "^https?://[^\\s]+$",
-              "pattern-description":
-                "Must be an http:// or https:// URL with no whitespace.",
-              "masked": false,
-              "copyable": false,
-            },
-            "default": [],
-            "range": "[0,10]",
-          },
-        },
-      },
     },
   },
 });