Remove duplicate copies of the db password setting

The same lines appear a few lines up from here.

lib/configuration.js

@@ -108,10 +108,6 @@ var conf = module.exports = convict({
       format: 'string?',
       env: 'DATABASE_NAME'
     },
-    password: {
-      format: 'string?',
-      env: 'MYSQL_PASSWORD'
-    },
     max_query_time_ms: {
       format: 'integer = 5000',
       doc: "The maximum amount of time we'll allow a query to run before considering the database to be sick",