Android: Removed native activity implementation. An activity with the same name based on a regular Activity is still in place for backwards compatibility reasons.
What does it mean?
Android: WebCam no longer works on Gingerbread devices
If I recall correctly, there used to be 2 types of activities that you could derive a Unity3d activity from (Android SDK). One was an older version that was for things prior to 2.3 and one was newer that had better input and other features called the NativePlayer. They kept the old version around long since they dropped < 2.3 support because of plugins and asset store packages that overrode the old version of the player activity.
The first change means you should use UnityPlayerActivity (derived from Activity) but not UnityPlayerNativeActivity (derived from NativeActivity). If you are not subclassing activities and overriding them in the manifest, this change won’t affect you.