Revert "Update NDK to r21." am: 8d9b20e7f8 am: 578234de9f am: c64046c9f0
Revert "Update NDK to r21." am: 8d9b20e7f8 am: 578234de9f am: c64046c9f0

Original change: https://android-review.googlesource.com/c/platform/external/perfetto/+/1500830

Change-Id: Ied129ae353c161414a119c7e48434c3f5c3cd7af

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto