Remove historic sources added to historic-imagery-index

Based on [discussion on talk-gb](https://lists.openstreetmap.org/pipermail/talk-gb/2013-October/015421.html) (and [next month](https://lists.openstreetmap.org/pipermail/talk-gb/2013-November/015453.html))

I added the sources to historic-imagery-index: https://github.com/osmlab/historic-imagery-index/commit/7e81ac7953b398b722e10ac553eb6e9f35c722ec

These have value for historic mapping, but not for OSM itself where there are more recent better aligned sources available.

Cross-reference https://github.com/osmlab/editor-imagery-index/issues/27#issuecomment-27620859