Remove non-ODbL compliant imagery sources

[Cobra]

Some tile providers (e.g. Mapquest open) have stopped updating before the redaction started and thus have a lot of cc-by-sa-only data in their tiles.
By using these tiles as background in osm people could copy redacted data back into the database, ruining the complete redaction effort.

I propose to remove these sources at least temporarily.

I do not want to remove them without any discussion. Are there any objections against removing them?
Do we want to take additional measures like auto-removing or blacklisting existing or custom imagery entries?

[stoecker]

I'm against this. There are many legitimate uses for these layers and they will get updated soon as well, so we will create more irritation then necessary when we drop them.