gossip: Fix tokens assignment in assassinate_endpoint
gossip: Fix tokens assignment in assassinate_endpoint

The tokens vector is defined a few lines above and is needed outsie the
if block.

Do not redefine it again in the if block, otherwise the tokens will be empty.

Found by code inspection.

Fixes #3551.

Message-Id: <e2c74eba6572e9b372ea5c53b7292fcd93425c5f@scylladb.com>

scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla