Can I remove a stollen iphone from tusted devices without turn off the activation lock

See If your iPhone, iPad, or iPod touch is lost or stolen https://support.apple.com/en-us/HT201472. And, see this heading If Find My [device] is enabled on your missing device. See step 6.

"Erase your device. To prevent anyone else from accessing the data on your missing device, you can erase it remotely. When you erase your device, all of your information (including credit, debit, or prepaid cards for Apple Pay) is deleted from the device, and you won't be able to find it using the Find My app or Find iPhone on iCloud.com. After you erase a device, you can't track it. If you remove the device from your account (i.e., from your device list) after you erase it, Activation Lock will be turned off. This allows another person to turn on and use your device."

Also, they still will be considered trusted until you remove them as mentioned above, but whether or not they are still trusted is not particularly relevant. You don't want to remove them from your account. See above.

If you mean that you want to stop tracking an old iPad in your iCloud account, there is a solution. But hopefully you had already signed out of it first.

Remember it's always better to de-authenticate your device and log out of everything and preferably wipe its memory before you give it away, dispose of it, etc. But if it's an emergency situation that you have little control over, the next best thing is to do a remote erase. But I will outline steps here.

Log into www.icloud.com and click on the Find iPhone app tile all the way in the lower righthand corner. Once in there at the center top, you'll see All Devices, and if you click on that it'll give you a list of any devices that were logged into that Apple ID. If your iPhone is still online and powered somewhere, you can click on that device and window will appear in the upper right corner with a few options. One of the options is to Erase iPad. This will logout your account out of that device and erase all of its contents.

If your iPhone is no longer online, in the center area where the devices are listed, that device will be greyed-out and show as Offline. In this case you can still click on it, and a different window will pop up with a few options. One of them is Remove From Account. This will simple unregister that device from your icloud account, so that you don't have to keep track of it anymore. There is also an option to Erase, but if the device.