Revert "Temporarily make binding controller no-op for visible bg users"

This reverts commit 2188e55b [1].

Reason for revert:
We are now ready to start launching IME for each active user in a
concurrent manner. The feature is now demoable.

 [1]: Ie8cea0888fab987d48410ae7638423f56d7029a2

Bug: 341558132
Bug: 344883373
Fix: 341558132
Test: presubmit
Flag: android.view.inputmethod.concurrent_input_methods
Change-Id: I3816401081a84c7765b2a0c150cc3a5544c95adb