I left out Torrent, and had one the PCs be a member of the resistance.
With hindsight, I should have left in her wand of cure light wounds!
In the fire forest, nothing really happens until the PCs reach the village (apart from the encounters with the devil, but those can occur anywhere). I think it also causes the perceived railroad problem - some players, in my view unfairly, think "We just get to march along the road and the DM runs through his list of random encounters". [I say unfairly because lots of D&D is like that, if the players only realised it

]
The trek upstream is a bit like that as well.
I think it would have been better if the Fire Forest was cut down a bit (pun not intentional) and then Act 1 of Shelter from the Storm could have been included as the last part of the second adventure instead of being part 1 of the third.
The second act of shelter from the storm has lots of optional encounters that happen if the PCs visit specific locations. You could leave them out, but in fact they were one of the parts my party enjoyed the most.
You could leave out the events on the way to Bresk in Mad King's Banquet. A remorhaz is a cool monster, but its appearance in southern Dassen was a real "what the heck is that doing here?" moment for my group, and I found the hanged man / halfling convoy thing a bit hard to follow.
The "destroy the catapults" scene in Mad King's Banquet was very tedious and I'll never run it again, but that's probably my fault as the DM for running a big set piece battle very badly. Its even put my story hour on hiatus, as I can't face writing it up. Expect the eventual write up of those two sessions to be about a paragraph long!
EDIT - after re-reading the above, I think I should point out that everyone in my group, myself included, is really enjoying War of the Burning Sky, most of which is excellent, and overall this has been one of the mosts enjoyable campaigns I've ever run!