Fix __ANDROID_API__ guards for libnativewindow

Partial revert of:
 - "Add __INTRODUCED_IN to <android/native_window.h>."
   commit a2c9607e.
 - "Add __INTRODUCED_IN annotations to <android/hardware_buffer.h>."
   commit 493f4a23

Most of these APIs were available via libandroid.so in API 9.

Bug: http://b/111668906
Bug: http://b/111660252
Test: m
Change-Id: I40874c4cd3413abf26f74f21caa5fb845fab721b
Merged-In: I40874c4cd3413abf26f74f21caa5fb845fab721b
(cherry picked from commit 733e443c)