Remove obsolete android ndk copy from //third_party/android_tools/ndk

It now lives at //third_party/android_ndk

Bug: 755920
Change-Id: I8ba6ee6cfb97fdca3aed3e43005f26ba540b3d61
Reviewed-on: https://chromium-review.googlesource.com/949098Reviewed-by: Shenghua Zhang <shenghuazhang@chromium.org>
Commit-Queue: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541185}

DEPS

@@ -1411,8 +1411,6 @@ hooks = [
 recursedeps = [
   # buildtools provides clang_format, libc++, and libc++abi
   'src/buildtools',
-  # android_tools manages the NDK.
-  'src/third_party/android_tools',
   # ANGLE manages DEPS that it also owns the build files for, such as dEQP.
   ("src/third_party/angle", "DEPS.chromium"),
   # src-internal has its own DEPS file to pull additional internal repos