Leave the wall built into the hillside unless you have damp problems there and if you do, removing the cement may not be the best solution. The other side of the wall is likely to be very damp and the cement may be all that is stopping it coming straight through the wall. Walls made of mud or wood don't like being wet but stone walls are generally happy.
The solution of course is to dig out the hillside behind the wall but this may not be possible. You may need to look at a dry lining solution / tanking solution.
The solution of course is to dig out the hillside behind the wall but this may not be possible. You may need to look at a dry lining solution / tanking solution.