fix: remove deprecated http-allow-sync-stalled from LH (#805)

The `--http-allow-sync-stalled` flag is deprecated as of Lighthouse
v5.3.0, with its behaviour being enabled by default.

In v6.0.0 we would like to remove the flag entirely, which requires
removing it from Kurtosis (which we run on our CI):

- https://github.com/sigp/lighthouse/pull/6490

src/cl/lighthouse/lighthouse_launcher.star

@@ -224,7 +224,6 @@ def get_beacon_config(
         "--http",
         "--http-address=0.0.0.0",
         "--http-port={0}".format(BEACON_HTTP_PORT_NUM),
-        "--http-allow-sync-stalled",
         "--slots-per-restore-point={0}".format(32 if constants.ARCHIVE_MODE else 8192),
         # NOTE: This comes from:
         #   https://github.com/sigp/lighthouse/blob/7c88f582d955537f7ffff9b2c879dcf5bf80ce13/scripts/local_testnet/beacon_node.sh