Good answers so far. Maybe realizing how and why the other 90% aren't there will help you out. I'm guessing that you think an average person has around 90-100% of this "humanity". They get scared when they hear of a terrorist attack on the news, they get sad when their grandfather dies. They get angry when someone throws trash on the street, they smile when they hear their friends had a baby. If I understand correctly, this would constitute emotions or humanity. You don't have those, but there are more specific situations that get you... anxious, perhaps? Maybe you have the inclination to get revenge even though you don't benefit from it except emotionally. Maybe you get jealous of other people's skill, wealth or recognition.
You don't want to lose the desire for wealth and comfort. You don't want to stop caring about the safety of your person. You don't want to lose your sense of humor or the ability to get lost in fantasy. These are also parts of humanity and emotionally driven; but I am correct in that you want to keep these, no? What, then, sets these apart from the 10% (5%, in my view, since you want to keep 5%) that you don't want to drag you down anymore? They don't require dependence on others aside from contracts. Imagine yourself in a situation where you were completely dependent on someone. Thinking about it feels bad, right? That might be why that 90% is gone, the interdependence involved in making an other's business your own is too painful. This is an okay theory, I hope, hand on a hot stove kind of thing.
The remaining 10(5)% probably isn't too hard to deal with. A chafing spot. You might never feel the urgency to get rid of it since you're obviously able to deal with it. Motivation is required to get rid of hard-wired human instincts like being obsessed with what others think of you, how other people in your environment are feeling, and so on. If the motivation isn't there and you haven't received strong genetic variations or trauma there's not really a reason why it would happen. As with developing muscles, the re-training of the emotional complex does not happen by "dropping and doing twenty" haphazardly.
I still think it's very possible to get rid of emotional reactions that you don't want to have. Unless a part of you is longing for connection and honesty and you actually don't enjoy a cold and robotic life deep down, with some practice (or as you mentioned, simple passage of time) this looks like a possible task.
I can share a personal example of my own deadening. Two emotional reactions that I have and don't want to have are anxiety about the future (it has decreased a good bit since I've decided on the field I'm going to be working in) and the need for what I until recently thought was physical intimacy (turns out it was actually emotional intimacy / communicational intimacy). The more specific emotional response to the unmet need being sadness. Both of these were stronger pulls five years ago and have been getting reduced with time. The reason being that they cause pain, if you do not act on the impulse (secure a future plan ASAP, get a girlfriend ASAP) then the brain will eventually devalue the emotional responses as less important. Like when doing aerobic exercise or meditating, once you adapt to the discomfort the feelings of aversion move to the back of your mind.
As other posters have pointed out, seeking out both understanding and actual experience of your trigger points will accelerate the numbing process. Exposure (at least accompanied by structure and wisdom) works. Now, what if the 5% are hard or impossible to bring out or experience? What if we don't really know what they are, even? We have a feeling that we're not robotic enough, we're suffering a bit, we're on edge unnecessarily, everything isn't just smoothly driving us into the grave like we'd hoped.
Then I propose going meta and handling these emotions as glitches. We're not robots, after all, we're at best some very early version of the Detroit: become human androids. This means that we're always going to have some bugs and broken parts, now what's the robotic way of dealing with our lack of inanimation? Acknowledging it and correcting trajectories for margins of error, not reacting to the reactions. This works even if we have no idea of why we feel some way, even. "Fatigue? I have enough physical energy to hit the gym anyways since I've been eating well." "Envy? Should I steam or boil the broccoli?"
