Move LogFile#remove_log_file_ftp FileDepotFtp#remove_file

https://bugzilla.redhat.com/show_bug.cgi?id=965889
LogFile#file_exists_ftp? is no longer needed

https://bugzilla.redhat.com/show_bug.cgi?id=965889
LogFile#build_path_ftp is no longer needed

https://bugzilla.redhat.com/show_bug.cgi?id=965889
LogFile#connect_ftp is no longer needed

https://bugzilla.redhat.com/show_bug.cgi?id=965889