Revert "pre-expansion gate label_break_value"

This reverts commit 137ded8ab1.

src/libsyntax/feature_gate/check.rs

@@ -518,6 +518,12 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                        "type ascription is experimental");
                 }
             }
+            ast::ExprKind::Block(_, opt_label) => {
+                if let Some(label) = opt_label {
+                    gate_feature_post!(&self, label_break_value, label.ident.span,
+                                    "labels on blocks are unstable");
+                }
+            }
             _ => {}
         }
         visit::walk_expr(self, e)

src/test/ui/feature-gates/feature-gate-label_break_value.rs

@@ -1,8 +1,5 @@
-#[cfg(FALSE)]
-pub fn foo() {
+pub fn main() {
     'a: { //~ ERROR labels on blocks are unstable
         break 'a;
     }
 }
-
-fn main() {}

src/test/ui/feature-gates/feature-gate-label_break_value.stderr

@@ -1,5 +1,5 @@
 error[E0658]: labels on blocks are unstable
-  --> $DIR/feature-gate-label_break_value.rs:3:5
+  --> $DIR/feature-gate-label_break_value.rs:2:5
    |
 LL |     'a: {
    |     ^^