systems/de0_nano: fix .system syntax

Remove simulation related options

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
systems/de1: fix .core and .system syntax

de1.core:

- remove leading spaces from simulator options
- add modelsim to the list of supported simulator

de1.system:

- Remove simulator related options

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>