cs: add “2390. Removing Stars From a String”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/removing-stars-from-a-string.cs

@@ -0,0 +1,18 @@
+public class Solution {
+    public string RemoveStars(string s) {
+        var sb = new StringBuilder();
+
+        foreach (var c in s) {
+            switch (c) {
+                case '*':
+                    sb.Remove(sb.Length - 1, 1);
+                    break;
+                default:
+                    sb.Append(c);
+                    break;
+            }
+        }
+
+        return sb.ToString();
+    }
+}