refactor(main): remove redundant extern crate declarations

src/main.rs

@@ -1,11 +1,7 @@
 #![feature(proc_macro_hygiene, decl_macro)]
 
-             extern crate clap;
-             extern crate handlebars;
-             extern crate ldap3;
 #[macro_use] extern crate clap;
 #[macro_use] extern crate rocket;
-             extern crate rocket_contrib;
 #[macro_use] extern crate serde_derive;
 #[macro_use] extern crate serde_json;