websocket.erl: Remove gratuitous call to rand:seed/1

[VlkrS]

crypto:strong_rand_bytes/1 doesn't need seeding:

"Generates N bytes randomly uniform 0..255, and returns the result in a binary. Uses a cryptographically secure prng seeded and periodically mixed with operating system provided entropy. By default this is the RAND_bytes method from OpenSSL."

https://www.erlang.org/docs/25/man/crypto#strong_rand_bytes-1