Don't #define __ANDROID_NDK__ for the platform build!

Caused an ODR violation trying to build current ToT of toybox.

Bug: N/A
Test: can successfully build code with `#ifdef __ANDROID_NDK__`
Change-Id: Ia80b8889b267779ee01f6257744e1794db0ebc65
diff --git a/libc/include/android/api-level.h b/libc/include/android/api-level.h
index ebce900..3a8f926 100644
--- a/libc/include/android/api-level.h
+++ b/libc/include/android/api-level.h
@@ -51,12 +51,6 @@
  * compiler/build system based on the API level you claimed to target.
  */
 #define __ANDROID_API__ __ANDROID_API_FUTURE__
-#else
-/**
- * `__ANDROID_NDK__` is defined for code that's built by the NDK
- * rather than as part of the OS.
- */
-#define __ANDROID_NDK__ 1
 #endif
 
 /** Names the Gingerbread API level (9), for comparisons against __ANDROID_API__. */