Comment 6 for bug 1928210

Running a conversion multiple times increases the number of fds in /proc.

Most of them are sockets, like

lrwx------ 1 mango mango 64 14. Mai 23:11 142 -> 'socket:[53142]'
lrwx------ 1 mango mango 64 14. Mai 23:11 145 -> 'socket:[72208]'
lrwx------ 1 mango mango 64 14. Mai 23:11 146 -> 'socket:[72209]'
lrwx------ 1 mango mango 64 14. Mai 23:11 149 -> 'socket:[53143]'
lrwx------ 1 mango mango 64 14. Mai 23:11 150 -> 'socket:[53144]'

by 34 for 17 files, so 2 socket fds for each pipeline.

Is something missing in _cleanup maybe?