Replaced sure() invocations with '!!' operator in libraries written on Kotlin.

libraries/sandbox/templatelib/src/TemplateHtml.kt

@@ -65,7 +65,7 @@ abstract class Tag(val name : String) : Element() {
   fun toString(): String {
     val builder = StringBuilder()
     appendTo(builder)
-    return builder.toString().sure()
+    return builder.toString()!!
   }
 }
 

libraries/sandbox/templatelib/src/TemplateJavaIo.kt

@@ -23,7 +23,7 @@ class WriterPrinter(val writer: Writer) : Printer {
 fun Template.renderToText(): String {
   val buffer = StringWriter()
   renderTo(buffer)
-  return buffer.toString().sure()
+  return buffer.toString()!!
 }
 
 fun Template.renderTo(writer: Writer): Unit {