You're right that it would conceptually make sense to have this tense. But there are some other syntax and vocabulary problems that I'll try to address, if you don't mind.
1) Having commented this function we have turned the reload function...
The phrase having commented this function has a meaning similar to after commenting this function. Substitute the latter for the former to see that it doesn't completely make sense in terms of time and focus:
2) After commenting this function, we have turned the reload function...
It would sound better to say:
3) Having commented this function, we then turned...
or
4) By commenting this function, we have turned...
I'll work with (4) since it also implies that the improvements resulted from this step, which seems to be your intended meaning. Your determiner that should be these or this since scroll bars is plural. You could also use the, especially if you aren't pointing at a certain set of scroll bars that are already immediately in focus (which would be difficult if they aren't appearing):
5) By commenting this function, we have turned the reload function quite less demanding in terms of CPU load, and consequently, the scroll bars are not appearing anymore.
The next issue is with your verb turned. The idea that you want here has to work with we [-----] it less demanding, and for that, you want to use made.
6) By commenting this function, we have made the reload function quite less demanding in terms of CPU load, and consequently, the scroll bars are not appearing anymore.
I think it sounds acceptable now. If you want to be a little clearer, you might try:
7) By commenting out this function, we have made the reload function much less demanding in terms of CPU load, and consequently, the scroll bars are not appearing anymore.
(I presume you commented out the first function. I would take commented to mean added comments to, but that doesn't make sense here if it reduced CPU load.)