revert DC live station locations

[mpadge]

Station location data for DC had to be hard-coded because the data given at opendata.dc.gov/datasets/capital-bike-share-locations became too unreliable, and simply returned an unknown error. Blame the underlying opendata.arcgis.com server! In the meantime, the data have been parked in R/sysdata.rda, but this can't be a long term solution as the system expands and changes. This issue is a flag to address this when (hopefully) the live data becomes more stable