When in doubt, just call Loki. Tom Hiddleston's performance as the God Of Mischief has been consistently excellent and a dependable source of fan goodwill for Marvel, which makes his absence since the God-awful Thor: The Dark World all the more annoying.
He's back for Thor: Ragnarok, but he was actually due for an earlier reappearance, as part of Thor's hallucination in Age Of Ultron - as Idris Elba rather naughtily revealed before release. Despite the confusing nature of Thor being given a glimpse of the future rather than a simple nightmarish vision (like his team-mates), he would have bumped into Loki the same way he did Heimdall in the dark Asgardian sequence.
Why It Was Cut
It gave away Loki's masquerade as Odin, in short. The vision would have seen Thor and Loki meet, with Thor asking what Odin would say to the mess. At that point, Hiddleston would have done his Anthony Hopkins impression, suggesting Thor was actually subconsciously aware of his brother's deception. Which would presumably ruin part of Thor: Ragnarok.
Why it hasn't reappeared as an extra is anyone's guess, but Marvel do have a tendency to hold back special features. Maybe we'll get a complete Phase 1-5 when it all fizzles out...?