Revert b0659e0ce28d08faf88cd9c4086bf9d2022ac85d.

This appears to cause a significant performance regression as shown in the
rotating Ocean example (http://bl.ocks.org/mbostock/6713736): performance went
from 60 FPS to 20 FPS.
Add world-countries.json to d3.geo.path benchmark.
Add Oceans to d3.geo.path benchmark.
Use higher-resolution files for benchmark.