GOG capped the game in two steps:
1) Using nvidia inspector to inject a 30FPS cap. This is only working with nvidia cards.
Because of the inspector "fix" not capping the game when using AMD or Intel cards they also fiddled with the executable file. When asking support they'll only tell you how to remove the inspector cap (I did so I know ;)). This is shown here and needs to be done first if you are using a nvidia GPU:
(In case you cannot find the directory where the nvidia inspector is stored - if you don't use Galaxy it is stored in the subfolder NI of the game's install directory.)
2) So far so good but the game remains capped because of the modification GOG did to the executable of the game.
Zyankali, a fellow GOG user, did a patcher to remove it completely. It is only possible due to his help to remove the final cap and I am very thankful. Download the patcher here:
Put it into the game directory, start it and click on "Patch it!". It will patch the executable file and also create a backup file in case sth. went wrong. In case you don't trust the file also take a look here:
So you can see that the file is clean even though some few scanners might give a false positive (unfortunately this happens sometimes with programs that are meant to patch files).
Even though there is no virus contained and the patcher is supposed to make a backup of the original executable please be aware that using this patcher happens at own risk. The same thing applies to removing the cap from the game. Sometimes the removal of the cap could lead to unwanted results (out of sync cutscenes ect.) that is the reason why GOG has introduced the cap at all.
Last but not least: if you want to have the optional removal of the cap officially please vote here: