Remove stale clang prebuilts and update clang-stable symlink.

Removing clang-3016494.
Removing clang-3217047.
Removing clang-3688880.
Reset clang-stable to point to clang-3859424.

Test: Build aosp/master and verified NDK is actually using
      both clang-3362437 and clang-2812033.

Change-Id: Ib5ad9a96fea560c60b8bfa0a974e698461021b62
510 files changed