[docs] Remove references to create-db.js script

Summary: Following D4151, the keyserver migration code should automatically setup the database when it sees the meta table is missing. As a result, it's no longer necessary for the user to manually call create-db.js.

Test Plan: As part of D4151 I tested that the database gets automatically set up if it has no tables

Reviewers: varun, palys-swm, yayabosh

Reviewed By: yayabosh

Subscribers: atul, Adrian, yayabosh

Differential Revision: https://phab.comm.dev/D4401