ksv: Clean up flag kAshEnableKeyboardShortcutViewer

The old keyboard overlay has been removed in M72 and
the flag kAshEnableKeyboardShortcutViewer is also removed.

Bug: 778874
Test: manual
Change-Id: I6ab9c350728c1e81f2d2437ac089187c4ab604c6
Reviewed-on: https://chromium-review.googlesource.com/c/1371073
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615567}

chrome/browser/flag_descriptions.cc

@@ -3119,11 +3119,6 @@ const char kAshEnableDisplayMoveWindowAccelsName[] =
 const char kAshEnableDisplayMoveWindowAccelsDescription[] =
     "Enable shortcuts for moving window between displays.";
 
-const char kAshEnableKeyboardShortcutViewerName[] =
-    "Enable keyboard shortcut viewer.";
-const char kAshEnableKeyboardShortcutViewerDescription[] =
-    "Enable keyboard shortcut viewer.";
-
 const char kAshEnableMirroredScreenName[] = "Enable mirrored screen mode.";
 const char kAshEnableMirroredScreenDescription[] =
     "Enable the mirrored screen mode. This mode flips the screen image "

chrome/browser/flag_descriptions.h

@@ -1871,9 +1871,6 @@ extern const char kAshDisableSmoothScreenRotationDescription[];
 extern const char kAshEnableDisplayMoveWindowAccelsName[];
 extern const char kAshEnableDisplayMoveWindowAccelsDescription[];
 
-extern const char kAshEnableKeyboardShortcutViewerName[];
-extern const char kAshEnableKeyboardShortcutViewerDescription[];
-
 extern const char kAshEnableMirroredScreenName[];
 extern const char kAshEnableMirroredScreenDescription[];