ci: simplify bazel fetch

Fixes: googleapis#6140

We only need to `bazel fetch ...`, which should get everything we need
for a `bazel build ...`. The extra packages that we previously had
listed were either redundant, or unnecessary, for example, a `bazel
build ...` never downloaded (or needed) `@go_sdk//...` in my local
experiments.

ci/cloudbuild/builds/lib/bazel.sh

@@ -32,19 +32,13 @@ io::log "Using bazelisk version"
 bazelisk version
 
 io::log "Prefetching bazel deps..."
-# Bazel downloads all the dependencies of a project, as well as a number of
-# development tools during startup. In automated builds these downloads fail
-# from time to time due to transient network problems. Running `bazel fetch` at
-# the beginning of the build prevents such transient failures from flaking the
-# build.
+# Prefetch all of the external dependencies that bazel will need. In automated
+# builds these downloads fail from time to time due to transient network
+# problems. Running `bazel fetch ...` at the beginning of the build prevents
+# such transient failures from flaking the build.
 TIMEFORMAT="==> 🕑 prefetching done in %R seconds"
 time {
-  "ci/retry-command.sh" 3 120 bazel fetch ... \
-    @local_config_platform//... \
-    @local_config_cc_toolchains//... \
-    @local_config_sh//... \
-    @go_sdk//... \
-    @remotejdk11_linux//:jdk
+  "ci/retry-command.sh" 3 120 bazel fetch ...
 }
 echo >&2