How to get the DDL for Oracle object without extra characters
The following will get rid of the LF and 2 spaces using a function though it would probably be better/easier to do it in your text editor.

select 
   REPLACE(dbms_lob.substr(
        dbms_metadata.get_ddl('FUNCTION','REMAP_SCHEMA', 'ETL'), 
      37, 1), CHR(10)||CHR(32)||CHR(32)||'CREATE','CREATE') text
   from dual


Obviously the first word that you are interested in keeping would need to be 'CREATE' for this to work. You could also use one of the REGEXP functions but I don't see that being any better/different to this method.
I'm also not sure why you particularly need to get rid of them.