Revert "[sets] Update unversioned set to use 4.14."

This reverts commit 8bf8c8ff36c935539debce048029f1a36ab6ebd0.
Revert "[Documentation/maintainers] Use 4.14 as basis for sets."

This reverts commit d6c0f4480aa10cbd12b3222417da0282e30a02e6.
[Documentation/maintainers] Add comment to clarify purpose of variable.