Remove IntelliJ Project Version Control

Alternatively, you can delete the vcs.xml which exist under the .idea folder;

.idea/vcs.xml

Just to add to the answers above. For one of my projects I had not only VCS (git) enabled, but also connected it to a remote repository. To start from a clean slate you can,

1. Go to File | Settings | Version Control and click -. This will disable the VCS and list it under Unregistered roots:
2. If you really want to get rid of that Unregistered roots: entry and all of the tracking information, go to your project folder and delete the ..\projectDir\.git\ folder also (provided that your were using git as your vcs)

Go to Settings (Preferences on macOS) | Version Control | Directory Mappings, select the mapping(s), click [-] icon or press Delete to remove the mapping or change the association to None.