ash: Clean up SetTabletModeEnabledForTest

The wait_for_completion parameter is unused. Remove it.

Bug: none
Change-Id: Ifef5cb2a3fab2cd96d7ce0515384b15c262c399d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625982
Auto-Submit: James Cook <[email protected]>
Commit-Queue: Xiaoqian Dai <[email protected]>
Reviewed-by: Xiaoqian Dai <[email protected]>
Cr-Commit-Position: refs/heads/master@{#843062}
diff --git a/ash/shell_test_api.cc b/ash/shell_test_api.cc
index a1f92006..94f7aaf 100644
--- a/ash/shell_test_api.cc
+++ b/ash/shell_test_api.cc
@@ -157,8 +157,7 @@
   return Shell::IsSystemModalWindowOpen();
 }
 
-void ShellTestApi::SetTabletModeEnabledForTest(bool enable,
-                                               bool wait_for_completion) {
+void ShellTestApi::SetTabletModeEnabledForTest(bool enable) {
   // Detach mouse devices, so we can enter tablet mode.
   // Calling RunUntilIdle() here is necessary before setting the mouse devices
   // to prevent the callback from evdev thread from overwriting whatever we set