throughout my explorations of Skyrim's files with the CK I have come across quite a large lists worth of cut content for Skyrim. while I doubt this is anywhere near all of it, it is interesting to see what was taken out before the game's completion none the less.

Quests with dialog remaining
-Research Thief(CoW)
-Missing Apprentices(CoW)
-Rogue Wizard(CoW)
-Supply Line(CoW)
-Animal Pelt Collection(Companions)
-Collecting the Edda(BC)
-Lod's Lot(FK)
-Runil's Dark Past(FK)

Quests with no dialog remaining
-NarzulburFreeFormWifeQuest
-freeform Markath a,b,c,f,g,h,i
-freeform solitue 5
-freeform Winterhold B
-Old Hroldan A
-A Bad Trade
-Trius' Trinket
-FreeformAngasMillKordirsSkooma

Quests that had parts cut
-Mephala's quest
-Boethiah's Bidding
-Tending the flames
-Vermina's quest

World interactions
-WE19, 26, 30
-WEDL09, 11
-WEJS5-8, 17, 27
-WERj08
-WIKill01, 02
-WIadditem 4-6
-WIchangelocation 6-7

Locations
-Windhelm Pit
-Wintersand Manor(wr)
-Barleydark Farm(wr)
-Maiden-Loom Manor(wr)
-Pathway Guard Tower(wr)
-Bear's cave mill(fk)
-Farrfalk Mansion(fk)
-The Lost Man's Reprieve(fk)
-Frost River Farm(hm)
-Riverwatch(em)
-Darkwater Crossing Crossing house
-Fort Blackmoor
-Iron tree mill
-Syncope Sanctuary
-Argi's Hut
-Gularz Khazgur keep
-Heljarchen
-The Longhouse in Stonehills

Items
-ring of khajiit

the two largest thing to have been cut are
1. The favor system, out of the 258+ favors BEthesda originally planned for, only 23ish remain
2. The civil war, which out of the 12 or so repeatable side quests originally inteded for the war, only 3 remain. furthermore, the civil war was non linear, and the enemy faction could take locations aswell.

Heljarchen came with the hearthfire DLC

The Heljarchen that was cut is unrelated to the Heljarchen home in Hearthfire.

Heljarchen was originally a small settlement that consisted of two farms, two normal houses, a blacksmith, and an apothecary, along with the nightgate in.

At least that is what appears to have been based on the keys left in the CK.