Exclude expired tickets in missed count.

[jrick]

Closes #371.

[jolan]

I think #371 came about because stake pools were showing tickets as missed when they were really expired. So there are actually two related parts of this:

1. getstakeinfo output
2. stakepooluserinfo output

So this fixes 1 but not 2. Happy to open another issue if you don't want to address that now though.

[jrick]

I'm not following. The results of stakepooluserinfo don't include any missed/expired counts.

[jolan]

There's a status field:

    {
      "status": "missed",
      "ticket": "652ce98dc0f9528ccd1a073b00851dc97caddc43fe2a10e8a0fbfe53c03eadab",
      "ticketheight": 1609,
      "spentby": "7704180e26fe4cda79ebe79a8a882cc952fcb4bbea94cfb3cb7d7c57aad233fb",
      "spentbyheight": 7770
    },

[jolan]

tOK

Will open a separate issue for stakepooluserinfo.