Remove Do Not Track option from Tor Browser privacy preferences
Global privacy options such as Do Not Track are fingerprinting vectors. In #5273 (closed), we discussed an alternate privacy UI for useful privacy options. A mockup of such UI will be added to the Tor Browser design doc. Given enough development resources, we should be able to migrate useful, yet fingerprintable browser behavior items from the current Firefox Privacy UI into that UI, and silo them on a per-site basis.
We came to the conclusion that the Do Not Track header is not a useful privacy option for Tor Browser, though. Given our threat model and privacy properties (https://www.torproject.org/projects/torbrowser/design/#privacy), it is only a vector for fingerprinting.
We can thus remove it at our earliest convenience.