Problem/Motivation The current theme system is a complicated mix of sub systems that pass data back and forth to one another in ways that confuses new users, and causes bugs. @see [#939462] We've solved many of these problems in Drupal 8 by re-architecting the theme layer, but sadly were not able to get everything done before code freeze. We've stopped using the preprocess hooks, and have deprecated them, but were not able to remove them in the Drupal 8 release cycle. @see [#2004872] Proposed resolution Remove the preprocess layer.

Proposed commit message: Issue #939462 by lauriii, Antti J. Salminen, NROTC_Webmaster, mbrett5062, tim.plunkett, tostinni, rteijeiro, dvessel, barraponto, theapi, joelpittet, cilefen, tuutti, drzraf, Fabianx, markcarver, xjm, catch, jenlampton, sun, effulgentsia, Cottser, davidhernandez, kscheirer, andypost, akalata, rooby, hass, fubhy, jhodgdon, lemunet, gleroux02, mike stewart, kevinquillen, MXT, mlncn, becw, PavanL, chriscalip: Specific preprocess functions for theme hook suggestions are not invoked General summary This is not considered a beta blocker or critical issue for D8.