Clipboard: Remove RuntimeEnabledFlag for Async Clipboard API.

The features gated by AsyncClipboard have launched in Chrome 66 and
Chrome 76. At this point, it's safe to assume the features will remain
launched.

Relevant chromestatus entries:
https://chromestatus.com/feature/5861289330999296
https://chromestatus.com/feature/5074658793619456

Change-Id: I5041570cea17385e72fc40c01b6dab26f69b4a03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2073467
Commit-Queue: Victor Costan <pwnall@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744597}

third_party/blink/renderer/modules/clipboard/clipboard.idl

@@ -9,8 +9,7 @@
     Exposed=Window
 ] interface Clipboard : EventTarget {
     [MeasureAs=AsyncClipboardAPIRead,
-     CallWith=ScriptState,
-     RuntimeEnabled=AsyncClipboard
+     CallWith=ScriptState
     ] Promise<sequence<ClipboardItem>> read();
 
     [MeasureAs=AsyncClipboardAPIReadText,
@@ -19,8 +18,7 @@
 
 
     [MeasureAs=AsyncClipboardAPIWrite,
-     CallWith=ScriptState,
-     RuntimeEnabled=AsyncClipboard
+     CallWith=ScriptState
     ] Promise<void> write(sequence<ClipboardItem> data);
 
     [MeasureAs=AsyncClipboardAPIWriteText,

third_party/blink/renderer/modules/clipboard/clipboard_item.idl

@@ -5,8 +5,7 @@
 // https://w3c.github.io/clipboard-apis/#clipboard-interface
 
 [
-  Exposed=Window,
-  RuntimeEnabled=AsyncClipboard
+  Exposed=Window
 ] interface ClipboardItem {
   [RaisesException] constructor(record<DOMString, Blob> items,
               optional ClipboardItemOptions options = {});

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -167,10 +167,6 @@
       name: "AspectRatioFromWidthAndHeight",
       status: "stable",
     },
-    {
-      name: "AsyncClipboard",
-      status: "stable",
-    },
     {
       name: "AudioOutputDevices",
       // Android does not yet support switching of audio output devices