Separate platform files and samples by API level.

Remove all duplicate platform files, i.e development/ndk/platforms/android-N now
only contains files that are introduced in API level 'N' and not found in level 'N-1'

(This makes it easier to manage independent platform release branches, and makes
 platform additions trivial to examine and maintain).

Move samples that depends on features of API level 'N' into platforms/android-N/samples

+ update tests/run-all.sh accordingly

Change-Id: I04c4c67c6c674c1714d5812d461d0524a4f4cfd9

ndk/platforms/android-9/samples/native-plasma/src/Dummy.java

@@ -0,0 +1,4 @@
+
+// Only needed for the build system.
+public class Dummy {
+}