Revert "launch: Disable autospawn by default when systemd daemon support is enabled."

This reverts commit 7276faca72e9696d4891daff139aee52509f43bf.

Using the new systemd socket activation for PulseAudio will cause PulseAudio to not
have any connection with D-Bus, breaking device reservation protocol, module-jackdbus-detect
and module-dbus-protocol. Therefore, autospawn is now still enabled by default even if you
build with systemd daemon headers.