IMPORTANT: For people reading the answer above, please do not try to edit your registry as the first thing you do. Editing the registry can cause unwanted and damaging side-effects on your system. If you need to remove the icon and you do have access to the tenant, please consider my answer below.
Optimally, it should be as simple as right clicking your OneDrive icon in the notification area of the taskbar, select "Settings", the "Account"-pane and click "Stop sync" for the library.
However, this may or may not work, depending on your current OneDrive client. A new client was "recently" released, but depending on a lot of things, you may still be stuck with the old one or have a missing connection.
Unfortunately, to remove the icon the easy way, you should still have access to the organization. If you do, no problem, if you don't then...
If you DO have access: First, update your OneDrive Synchronization client. The easiest way to do this is to do a so called "Online repair" as described here. This will give you the most recent client.
Then, just click Start, type "OneDrive" so the "OneDrive desktop app" appears, then enter your username and password for the organization that you have synced with. This will overwrite the old connection with a new one. NOW you can right-click the icon, click "Settings", select the "Account"-pane and choose "Stop syncing" and the icon will be gone from your Explorer.
If you don't have access however, then it is quite possible you must walk the eerie trail of the regedit. You can research a lot of it online, this should help you along the way, this might also prove interesting.