Relax strict ActionMode instance checking when finishing action modes

In previous platform versions, finishing an action mode would clean up
the current action mode even if it was not the same ActionMode
instance. Some common shared code inadvertently relied on this
behavior, so stay bug-compatible with it based on targetSdkVersion.
New apps will get the stricter behavior.

Bug 22265882

Change-Id: Id5d6341aefc07a3cb788d5d6d0b531816f761e42