Drop milstein, extended-grid coders and address field

[danvk]

Closes #165

Data update: oldnyc/oldnyc.github.io@61289d0

Net loss of 98 photos from the site. Many of these were in debatable locations. I hope to get at least some of them back with #166.

This removes 860 more files from the geocache — fewer than I would have expected!

Truth stats are very good:

Before:
    208 / 269 = 77.32% of locatable images correctly located.
      9 / 217 = 4.15% incorrectly located.

After:
    208 / 269 = 77.32% of locatable images correctly located.
      7 / 215 = 3.26% incorrectly located.