Update incorrect error code docs

src/librustc_error_codes/error_codes/E0493.md

-A type with a `Drop` implementation was destructured when trying to initialize
-a static item.
+A value with a custom `Drop` implementation may be dropped during const-eval.
 
 Erroneous code example:
 
@@ -16,13 +15,14 @@ struct Foo {
     field1: DropType,
 }
 
-static FOO: Foo = Foo { ..Foo { field1: DropType::A } }; // error!
+static FOO: Foo = Foo { field1: (DropType::A, DropType::A).1 }; // error!
 ```
 
 The problem here is that if the given type or one of its fields implements the
-`Drop` trait, this `Drop` implementation cannot be called during the static
-type initialization which might cause a memory leak. To prevent this issue,
-you need to instantiate all the static type's fields by hand.
+`Drop` trait, this `Drop` implementation cannot be called within a const
+context since it may run arbitrary, non-const-checked code. To prevent this
+issue, ensure all values with custom a custom `Drop` implementation escape the
+initializer.
 
 ```
 enum DropType {