To elaborate, the intent is that only abilities that consume Runes give Runic Power. Chill of the Grave increased the runic power generations of certain abilities. Since a Rime Proc Howling Blast proc would generally generate no Runic Power, Chill of the Grave would have still increased it's runic power generation (by 10, wasn't it?), so a Rime-powered Howling Blast would have generated 10 runic power. Since Chill of the Grave is gone, Rime procs are now generating its baseline 0 runic power.