Revert "add PIDFile directive to systemd service"
Revert "add PIDFile directive to systemd service"

This reverts commit 19c095a8172441690f30a21e70f73a0ec8475b2f.

See discussion at #375 for details.

icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2