Lint on redundant trailing semicolon after item

We now lint on code like this:

```rust
fn main() {
    fn foo() {};
    struct Bar {};
}
```

Previously, this caused warnings in Cargo, so it was disabled.

src/test/ui/lint/redundant-semicolon/item-stmt-semi.rs

@@ -1,10 +1,6 @@
-// check-pass
-// This test should stop compiling
-// we decide to enable this lint for item statements.
-
 #![deny(redundant_semicolons)]
 
 fn main() {
-    fn inner() {};
-    struct Bar {};
+    fn inner() {}; //~ ERROR unnecessary
+    struct Bar {}; //~ ERROR unnecessary
 }

src/test/ui/lint/redundant-semicolon/item-stmt-semi.stderr

@@ -0,0 +1,20 @@
+error: unnecessary trailing semicolon
+  --> $DIR/item-stmt-semi.rs:4:18
+   |
+LL |     fn inner() {};
+   |                  ^ help: remove this semicolon
+   |
+note: the lint level is defined here
+  --> $DIR/item-stmt-semi.rs:1:9
+   |
+LL | #![deny(redundant_semicolons)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: unnecessary trailing semicolon
+  --> $DIR/item-stmt-semi.rs:5:18
+   |
+LL |     struct Bar {};
+   |                  ^ help: remove this semicolon
+
+error: aborting due to 2 previous errors
+