Rename *.jet -> *.kt in codegen tests

compiler/testData/codegen/controlStructures/tryFinally.kt

@@ -0,0 +1,9 @@
+fun f(sb: StringBuilder, s: String): Unit {
+  try {
+    sb.append("foo");
+    sb.append(Integer.parseInt(s));
+  }
+  finally {
+    sb.append("bar");
+  }
+}