Adjust PSI usages to new labels syntax

compiler/frontend/src/org/jetbrains/kotlin/psi/JetExpressionWithLabel.kt

@@ -25,11 +25,7 @@ open public class JetExpressionWithLabel(node: ASTNode) : JetExpressionImpl(node
             findChildByType<JetContainerNode>(JetNodeTypes.LABEL_QUALIFIER)?.
             findChildByType(JetNodeTypes.LABEL) as? JetSimpleNameExpression
 
-    public fun getLabelName(): String? {
-        val labelElement = getTargetLabel()
-        assert(labelElement == null || labelElement.getText().startsWith("@"))
-        return labelElement?.getText()?.substring(1)
-    }
+    public fun getLabelName(): String? = getTargetLabel()?.getIdentifier()?.getText()
 
     override fun <R, D> accept(visitor: JetVisitor<R, D>, data: D) = visitor.visitExpressionWithLabel(this, data)
 }

compiler/frontend/src/org/jetbrains/kotlin/psi/JetLabelReferenceExpression.kt

@@ -21,5 +21,5 @@ import org.jetbrains.kotlin.lexer.JetTokens
 import com.intellij.psi.PsiElement
 
 public class JetLabelReferenceExpression(node: ASTNode) : JetSimpleNameExpressionImpl(node) {
-     public override fun getReferencedNameElement() = (findChildByType(JetTokens.LABEL_IDENTIFIER): PsiElement?) ?: this
+     public override fun getReferencedNameElement() = getIdentifier() ?: this
 }

compiler/frontend/src/org/jetbrains/kotlin/psi/JetPsiUtil.java

@@ -839,8 +839,7 @@ public class JetPsiUtil {
     }
 
     public static boolean isLabelIdentifierExpression(PsiElement element) {
-        return element instanceof JetSimpleNameExpression &&
-               ((JetSimpleNameExpression) element).getReferencedNameElementType() == JetTokens.LABEL_IDENTIFIER;
+        return element instanceof JetLabelReferenceExpression;
     }
 
     @Nullable