Remove support for the special "assets" directory.

sdk/lib/_internal/pub/test/serve/web_socket/url_to_asset_id_test.dart

Index: sdk/lib/_internal/pub/test/serve/web_socket/url_to_asset_id_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/web_socket/url_to_asset_id_test.dart b/sdk/lib/_internal/pub/test/serve/web_socket/url_to_asset_id_test.dart
index 74726bf10daeafe948a81b5b4c01fc7c23d34929..9bc2392350b9148a511e02885e62d62c239a865d 100644
--- a/sdk/lib/_internal/pub/test/serve/web_socket/url_to_asset_id_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/web_socket/url_to_asset_id_test.dart
@@ -15,12 +15,6 @@ main() {
   setUp(() {
     d.dir("foo", [
       d.libPubspec("foo", "0.0.1"),
-      d.dir("asset", [
-        d.file("foo.txt", "foo"),
-        d.dir("sub", [
-          d.file("bar.txt", "bar"),
-        ])
-      ]),
       d.dir("lib", [
         d.file("foo.dart", "foo")
       ])
@@ -100,23 +94,4 @@ main() {
     }, {"package": "foo", "path": "lib/foo.dart"});
     endPubServe();
   });
-
-  integration("converts URLs to matching asset ids in the entrypoint's asset/",
-      () {
-    // Paths in asset/.
-    pubServe(shouldGetFirst: true);
-    expectWebSocketResult("urlToAssetId", {
-      "url": getServerUrl("web", "assets/foo/foo.txt")
-    }, {"package": "foo", "path": "asset/foo.txt"});
-    endPubServe();
-  });
-
-  integration("converts URLs to matching asset ids in a dependency's of asset/",
-      () {
-    pubServe(shouldGetFirst: true);
-    expectWebSocketResult("urlToAssetId", {
-      "url": getServerUrl("web", "assets/foo/sub/bar.txt")
-    }, {"package": "foo", "path": "asset/sub/bar.txt"});
-    endPubServe();
-  });
 }