[2.5][Process] Do not redirect output to file handles when output is disabled, simply discard it

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
ProcessPipes are not supposed to be used by anybody. This is actually a *private* part of Process. I understand this is a bc break in a strict consideration, but I do not consider it breaking anything for people.

For the record, I propose to break BC in this class here again https://github.com/symfony/symfony/pull/10934/files

Should I really provide BC for this one? What other people think?