Delete tester images (#5091)

Progrollout replaced it.
Fixes: #4320

Author: jonathanmetzman

docker/build-immutable.sh

@@ -23,7 +23,6 @@ IMAGES=(
   gcr.io/clusterfuzz-images/base/immutable
   gcr.io/clusterfuzz-images/chromium/base/immutable
   gcr.io/clusterfuzz-images/chromium/builder/immutable
-  gcr.io/clusterfuzz-images/chromium/tester/immutable
   gcr.io/clusterfuzz-images/tworker/immutable
   gcr.io/clusterfuzz-images/utask-main-scheduler/immutable
   gcr.io/clusterfuzz-images/fuchsia/immutable

docker/build.sh

@@ -19,7 +19,6 @@ IMAGES=(
   gcr.io/clusterfuzz-images/chromium/base
   gcr.io/clusterfuzz-images/chromium/builder
   gcr.io/clusterfuzz-images/chromium/high-end
-  gcr.io/clusterfuzz-images/chromium/tester
   gcr.io/clusterfuzz-images/chromium/tests-syncer
   gcr.io/clusterfuzz-images/oss-fuzz/base
   gcr.io/clusterfuzz-images/oss-fuzz/host-high-end