Remove legacy smallfiles flag for MongoDB

[duffn]

--smallfiles was removed in version 4.2: https://docs.mongodb.com/manual/release-notes/4.2/#mmapv1-specific-configuration-options. Since the latest tag is specified, the database now fails to startup.

Starting mongodb ... done
Starting go-clean-architecture ... done
Attaching to mongodb, go-clean-architecture
mongodb    | Error parsing command line: unrecognised option '--smallfiles'
mongodb    | try 'mongod --help' for more information

[evan-sm]

+1 confirm