drop unnecessary "warning" from warning text

Author: QuietMisdreavus

src/librustdoc/lib.rs

@@ -649,7 +649,7 @@ where R: 'static + Send,
         let diag = core::new_handler(error_format, None);
 
         fn report_deprecated_attr(name: &str, diag: &errors::Handler) {
-            let mut msg = diag.struct_warn(&format!("WARNING: the `#![doc({})]` attribute is \
+            let mut msg = diag.struct_warn(&format!("the `#![doc({})]` attribute is \
                                                      considered deprecated", name));
             msg.warn("please see https://github.com/rust-lang/rust/issues/44136");
 

src/test/rustdoc-ui/deprecated-attrs.stderr

@@ -1,9 +1,9 @@
-warning: WARNING: the `#![doc(no_default_passes)]` attribute is considered deprecated
+warning: the `#![doc(no_default_passes)]` attribute is considered deprecated
   |
   = warning: please see https://github.com/rust-lang/rust/issues/44136
   = help: you may want to use `#![doc(document_private_items)]`
 
-warning: WARNING: the `#![doc(passes = "...")]` attribute is considered deprecated
+warning: the `#![doc(passes = "...")]` attribute is considered deprecated
   |
   = warning: please see https://github.com/rust-lang/rust/issues/44136