"Relicensing Unfinished W3C Specifications" to move to the CMS

[vivienlacourba]

As discussed when redesigning the W3C guidebook (w3c/guide#290 (comment)) the page https://www.w3.org/2014/12/relicense.html should be moved to the CMS under https://www.w3.org/policies/specification-relicense/

@koalie let me know when done and I'll create the redirect and remove the legacy file.

cc: @plehegar