Retire LOCAL_NDK_VERSION.

We are now unifying the NDK versions of unbundled native code to always
use the latest NDK.
We don't need the variable LOCAL_NDK_VERSION now.
To build native code with NDK, you need set just LOCAL_SDK_VERSION.

Bug: 6932421
Change-Id: I86f05a264249cda6bae97b4b1616f03700cd9dfa
diff --git a/core/shared_library.mk b/core/shared_library.mk
index ab7480d..122cd29 100644
--- a/core/shared_library.mk
+++ b/core/shared_library.mk
@@ -46,7 +46,7 @@
 my_target_libgcc := $(TARGET_LIBGCC)
 my_target_crtbegin_so_o := $(TARGET_CRTBEGIN_SO_O)
 my_target_crtend_so_o := $(TARGET_CRTEND_SO_O)
-ifdef LOCAL_NDK_VERSION
+ifdef LOCAL_SDK_VERSION
 # Make sure the prebuilt NDK paths are put ahead of the TARGET_GLOBAL_LD_DIRS,
 # so we don't have race condition when the system libraries (such as libc, libstdc++) are also built in the tree.
 my_target_global_ld_dirs := \