Remove redundant webidl_must_inherit compiler plugin lint

At first I was considering moving it to a procedural macro
(source-level information should be sufficient),
and started by trying to reproduce the error case
by changing `htmldivelement.rs` to use `Element` instead of `HTMLElement`
as the first field.

The output was:

```rust
error[E0308]: mismatched types
   --> /home/simon/servo2/target/debug/build/script-4caa244faca7d10f/out/Bindings/HTMLDivElementBinding.rs:665:31
    |
665 |         let _: &HTMLElement = self.as_parent();
    |                               ^^^^^^^^^^^^^^^^ expected struct `dom::htmlelement::HTMLElement`, found struct `dom::element::Element`
    |
    = note: expected type `&dom::htmlelement::HTMLElement`
               found type `&dom::element::Element`
```

This line number is inside a generated method called `__assert_parent_type`.
As far as I can tell, any case where this lint would error is already caught
by such methods. The lint is therefore redundant and can safely be removed.

1 files changed, 1 insertions, 2 deletions

diff --git a/components/script/Cargo.toml b/components/script/Cargo.toml
index 6eec808b8df..5c9fa86e95f 100644
--- a/components/script/Cargo.toml
+++ b/components/script/Cargo.toml
@@ -16,8 +16,7 @@ path = "lib.rs"
 debugmozjs = ['js/debugmozjs']
 profilemozjs = ['js/profilemozjs']
 unrooted_must_root_lint = ["script_plugins/unrooted_must_root_lint"]
-webidl_lint = ["script_plugins/webidl_lint"]
-default = ["unrooted_must_root_lint", "webidl_lint"]
+default = ["unrooted_must_root_lint"]
 webgl_backtrace = ["backtrace", "canvas_traits/webgl_backtrace"]
 js_backtrace = ["backtrace"]
 uwp = ["js/uwp"]