Revert "man: add note about systemd-vconsole-setup.service and tty as input/output"

This reverts commit 0b578036.

From https://github.com/systemd/systemd/pull/16503#issuecomment-660212813:
systemd-vconsole-setup (the binary) is supposed to run asynchronously by udev
therefore ordering early interactive services after systemd-vconsole-setup.service
has basically no effect.

Let's remove this paragraph. It's better to say nothing than to give pointless
advice.