Remove rustc-dev from the default nightly components

It was already filtered from other branches, but we only kept it in
nightly's default to ease the transition. Now that the separation of
rust-std/rustc-dev has reached the 1.40 release, it seems like a good
time for that transition to end.

src/tools/build-manifest/src/main.rs

@@ -453,10 +453,10 @@ impl Builder {
             "lldb-preview", "rust-analysis", "miri-preview"
         ]);
 
-        // The compiler libraries are not stable for end users, but `rustc-dev` was only recently
-        // split out of `rust-std`. We'll include it by default as a transition for nightly users.
+        // The compiler libraries are not stable for end users, and they're also huge, so we only
+        // `rustc-dev` for nightly users, and only in the "complete" profile. It's still possible
+        // for users to install the additional component manually, if needed.
         if self.rust_release == "nightly" {
-            self.extend_profile("default", &mut manifest.profiles, &["rustc-dev"]);
             self.extend_profile("complete", &mut manifest.profiles, &["rustc-dev"]);
         }
     }
@@ -514,15 +514,6 @@ impl Builder {
             components.push(host_component("rust-mingw"));
         }
 
-        // The compiler libraries are not stable for end users, but `rustc-dev` was only recently
-        // split out of `rust-std`. We'll include it by default as a transition for nightly users,
-        // but ship it as an optional component on the beta and stable channels.
-        if self.rust_release == "nightly" {
-            components.push(host_component("rustc-dev"));
-        } else {
-            extensions.push(host_component("rustc-dev"));
-        }
-
         // Tools are always present in the manifest,
         // but might be marked as unavailable if they weren't built.
         extensions.extend(vec![
@@ -542,7 +533,6 @@ impl Builder {
         );
         extensions.extend(
             HOSTS.iter()
-                .filter(|&&target| target != host)
                 .map(|target| Component::from_str("rustc-dev", target))
         );
         extensions.push(Component::from_str("rust-src", "*"));