Revert of CQ: Remove android_arm64_rel trybot (patchset #1 id:1 of https://codereview.webrtc.org/2270943003/ )

Reason for revert:
The machine seems healthy again.

Original issue's description:
> CQ: Remove android_arm64_rel trybot
>
> The bot is having problems again.
>
> NOTRY=true
> BUG=634266
> TBR=ehmaldonado@webrtc.org
>
> Committed: https://crrev.com/24ee05016ccb1c1ea05c4b646fb29e2cefbfe439
> Cr-Commit-Position: refs/heads/master@{#13874}

TBR=ehmaldonado@webrtc.org
NOTRY=true
BUG=634266

Review-Url: https://codereview.webrtc.org/2277263002
Cr-Commit-Position: refs/heads/master@{#13923}
diff --git a/infra/config/cq.cfg b/infra/config/cq.cfg
index 15ccd3e..02250f4 100644
--- a/infra/config/cq.cfg
+++ b/infra/config/cq.cfg
@@ -28,7 +28,7 @@
       name: "master.tryserver.webrtc"
       builders { name: "android_dbg" }
       builders { name: "android_rel" }
-      # builders { name: "android_arm64_rel" }
+      builders { name: "android_arm64_rel" }
       builders { name: "android_clang_dbg" }
       builders { name: "android_compile_mips_dbg" }
       builders { name: "android_compile_x86_dbg" }