Remove ImeFocusController#set{Served, NextServed}View

As ImeFocusController#set{Served, NextServed}View originally exposes to
InputMethodManager is only for clearing the served view in
IMM#finishInputLocked() with a special code logic:

```
  setNextServedView(null);
  if (getServedView() != null) {
      // do finish input
     setServedView(null);
  }
```

which isn't necessary and can be clean-up with a method to notify
ImeFocusController to clear the served / next served view, then doing
the rest of finshing logic when the method has cleared the served view:

```
if (controller.clearServedViewsLocked() != null) {
    // do finish input
}
```

With this change, we can simply remove the set{Served, NextServed}View
to get rid of this dependency with InputMethodManager.

Bug: 244504062
Test: atest CtsInputMethodTestCases

Change-Id: Ibcde35765c0e2e6c372aa64dbc7e774a8d860543