Not entirely, of course. Think about the parts of the tank that wear out the most: the engine, the tracks, the road wheels. A tank can be immobilized by broken parts, and waste a perfectly good gun in the process. If you have a bunch of broken or nearly broken tanks, might as well drop them off somewhere they can be useful. Also, dig them into the ground, since they're not going anywhere anyway.
The following photos show some more MS-1s. These are armed with 45 mm guns, and have their "tails" removed. They haven't been dug into the ground yet, but they are going to be.
Pre-war light tanks weren't the only ones to end up in the ground. A letter from the GAZ factory to GABTU from 1942 talks about 379 hulls for obsolete T-40 and T-60 tanks, and states that 150 hulls are available to GABTU to use as pillboxes.
Of course, not only light tanks became obsolete. Another letter to GABTU, this time from a tank school, states: "The school has 4 T-35 tanks and 8 T-28 tanks, which, after long use and numerous repairs, have become unusable and cannot be restored with the resources of the school. I await your instructions regarding transfer of these tanks to the armoured train directorate in order to install them as weapons platforms or immobile gun batteries in fortified regions." This letter was sent in 1943, long after those tanks would have been useful in combat. Let's see how this turned out: