[fenix] Bug 1674186 - Use shippable platforms for Browsertime tests. (https://github.com/mozilla-mobile/fenix/pull/16261)

* Use shippable platforms.

* Undo testing changes.

taskcluster/ci/browsertime/kind.yml

@@ -43,8 +43,8 @@ job-defaults:
         tier: 2
         platform:
             by-abi:
-                arm64-v8a: android-hw-p2-8-0-android-aarch64/opt
-                armeabi-v7a: android-hw-g5-7-0-arm7-api-16/opt
+                arm64-v8a: android-hw-p2-8-0-android-aarch64-shippable/opt
+                armeabi-v7a: android-hw-g5-7-0-arm7-api-16-shippable/opt
     worker-type:
         by-abi:
             armeabi-v7a: t-bitbar-gw-perf-g5