Is there are a way to restore System schema to it's original state? I've installed Oracle 11g Database Enterprise Edition and my task was to import schemas. I'm totally new so I ran command: 

imp system/password file=path.dmp full=y


And import everything (10 dumps, 150+ tables) into System schema. Could I restore this Schema to original state without reinstalling database? Or maybe you could delete directory with all of this tables and reinstall database, without harming listeners and tnsnames.ora?
There is no way to restore SYSTEM schema to the original state of empty database if you haven't backups, so you should recreate database. You could do this with Database Configuration Assistant (I'm using Windows Server 2012): run it, select delete database option, select database you want to delete, enter password to dba user and execute it.

After this you could recreate database with options you need.