syz-manager: hide the "Crashes" table if reporting to dashboard

[ramosian-glider]

When syzkaller is running stand-alone, it has a list of crashes on the status page, that is up-to-date and contains the crashes detected during the current invocation.

However when a syzkaller instance reports crashes to syz-ci, the list of crashes on the status page is usually stale (e.g. today for most instances reporting to syzbot.appspot.com the crashes date back to 2021-2022).

I suggest hiding the "Crashes" table altogether if the syzkaller instance is connected to syz-ci.

[dvyukov]

The idea behind saving these crashes was to give at least some visibility into what was lost. If we are not showing them, then it's easier to just not save them entirely. Perhaps managers should instead try to report an error the dashboard instead.