We want to swap out all 8 cores LUCI perf tester with 32 cores to improve the speed of uploading (also see issue 857283).

Since we don't have any 32 cores machine left, I plan to switch android-arm64-builder-perf which is  using 18 32-cores machines to use 32 8-core machines instead. 

I has confidence that this should work because:
*Building android-arm64 with 8 cores take about ~33 minutes in https://ci.chromium.org/buildbot/chromium.perf/Android%20arm64%20Compile%20Perf/
* Building android with 8 cores take about 10 minutes, and only require 10 bots to fill all the Chromium commit load.
* so by tripling the number of bots building android, we should be able to use 8 cores for building android-arm64


Doing this will give us 18 32-cores Linux machines back, which should be more than enough to fill all the Linux perf testers.