It should be noted that there are multiple mechanics at play here, and neither was removed completely.
The first mechanic is that while jumping, when you either hold down the A-button and move your mouse left at the right pace, or hold down the D-button and move your mouse right at the right pace, you will accelerate slightly, plus change your trajectory.
The second mechanic is that you don't just stop when you hit the ground, instead friction is applied to you in a very simplistic way. Also, when you jump at exactly the same tick at which you hit the ground, this friction won't even be applied.
Both mechanics together mean that you can reach theoretically unlimited velocity.
I'm not entirely sure what the changes in 1.3 were, but certainly both mechanics still exist in 1.6.
The first mechanic you can easily test on a local server, by typing "sv_gravity 0" into the console, then jumping into the air and performing the motions mentioned above - you can still reach unlimited speed.
The second mechanic is harder to test, but I'm pretty sure it still works. However, it might only work for a single time or something like that.
There is also "sv_airaccelerate" which somehow controls how much you accelerate with mechanic 1, but I'm not exactly sure how it works.
One thing though that I always mention when this comes up: Mechanic 1 doesn't just make gameplay better, it actually makes it more realistic too, and it should be implement in every shooter. "But I can't jump around corners in real life!" you might say, however I would argue that you actually can. We can do this because we can use both of our feet to manipulate our trajectory much more finely that we can in most games.
All mechanic one does is give us this lost freedom of motion back.