Remove id field from session_tokens

[wqyeo]

Title,

remove the id field from session_tokens, and form a composite primary key with account_id and session_token instead.

Alternatively

Set session_token field as primary key, and index account_id.

[wqyeo]

Welp, some functions rely on the id field of account_sessions to do joins and stuff, so...

Willing to accept a PR if anyone wants to do this enhancement lol