op-reth: emit --disable-discovery (not --nodiscover) for node_sync nodes

op-reth rejects geth's --nodiscover flag, which the op-geth base template
emits for node_sync nodes. Use reth's --disable-discovery instead.

- hashkeychain-testnet: now node_sync/consensus-layer (was execution-layer
  with an empty DB, which could not backfill) + --disable-discovery
- xlayer mainnet/testnet (archive+pruned): --nodiscover -> --disable-discovery
  (these were latently broken on restart)

Fix lives in the op-reth.yml base template so all reth nodes are covered;
the redundant override in op-reth.boba.yml was removed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

op/reth/xlayer-testnet-op-reth-pruned-trace.yml

@@ -73,12 +73,12 @@ services:
       - --chain=/config/genesis.json
       - --config=/config/reth/reth.toml
       - --datadir=/root/.local/share/reth
+      - --disable-discovery
       - --engine.cross-block-cache-size=${XLAYER_TESTNET_RETH_STATE_CACHE:-4096}
       - --full
       - --max-inbound-peers=50
       - --max-outbound-peers=50
       - --metrics=0.0.0.0:9001
-      - --nodiscover
       - --rollup.sequencer-http=https://testrpc.xlayer.tech
       - --rpc-cache.max-blocks=10000
       - --rpc-cache.max-concurrent-db-requests=2048