Remove redundant additional checks

[duncandewhurst]

The following additional checks are no longer required for OFDS 0.4 because the rules are now encoded in the schema:

• https://libcoveofds.readthedocs.io/en/latest/checks.html#node-location-type-is-point
• https://libcoveofds.readthedocs.io/en/latest/checks.html#node-location-coordinates-format-is-a-single-position
• https://libcoveofds.readthedocs.io/en/latest/checks.html#span-route-type-is-linestring
• https://libcoveofds.readthedocs.io/en/latest/checks.html#span-route-coordinates-is-an-array-of-positions

[duncandewhurst]

This isn't urgent for the 0.4 release.