[ddc] Delete unused imports in dart:_runtime

- Delete the `spread()` implementation because it is never used.

Change-Id: I7b33a2fc981801608c08aa356ff9c8fb879902c2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/383682
Commit-Queue: Nicholas Shahan <[email protected]>
Reviewed-by: Nate Biggs <[email protected]>

Author: nshahan

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/runtime.dart

@@ -6,8 +6,6 @@
 library dart._runtime;
 
 import 'dart:async';
-import 'dart:collection';
-
 import 'dart:_debugger' show stackTraceMapper, trackCall;
 import 'dart:_foreign_helper'
     show
@@ -18,8 +16,7 @@ import 'dart:_foreign_helper'
         JS_GET_NAME,
         JSExportName,
         rest,
-        TYPE_REF,
-        spread;
+        TYPE_REF;
 import 'dart:_interceptors'
     show
         JavaScriptBigInt,
@@ -44,33 +41,28 @@ import 'dart:_js_helper'
         getRtiForRecord,
         ImmutableMap,
         ImmutableSet,
-        JsLinkedHashMap,
         jsObjectGetPrototypeOf,
         jsObjectSetPrototypeOf,
         NoReifyGeneric,
         notNull,
         Primitives,
         PrivateSymbol,
         ReifyFunctionTypes,
-        TypeErrorImpl,
-        undefined;
+        TypeErrorImpl;
 import 'dart:_js_shared_embedded_names';
 import 'dart:_rti' as rti
     show
         bindingRtiFromList,
         constructorRtiCachePropertyName,
         createRuntimeType,
-        findType,
         getFunctionParametersForDynamicChecks,
         getGenericFunctionBounds,
-        getLegacyErasedRti,
         getRecordTypeElementTypes,
         getRecordTypeShapeKey,
         instanceType,
         instantiatedGenericFunctionType,
         interfaceTypeRecipePropertyName,
         isGenericFunctionType,
-        isNullable,
         isRecordType,
         isSubtype,
         Rti,

sdk/lib/_internal/js_dev_runtime/private/foreign_helper.dart

@@ -261,11 +261,6 @@ class _Rest {
 
 const _Rest rest = _Rest();
 
-dynamic spread(args) {
-  throw StateError('The spread function cannot be called, '
-      'it should be compiled away.');
-}
-
 /// Reads an embedded global.
 ///
 /// The [name] should be a constant defined in the `_js_shared_embedded_names`