Enable few downstream projects rules_android, Bazelisk, Gerrit (#1935)

Enable projects from disabled pipeline to Downstream pipeline

- rules_android :
https://buildkite.com/bazel/bazel-at-head-plus-disabled/builds/1993#018e7e82-0c63-41b7-9372-3265d71a50a2

- Bazelisk :
https://buildkite.com/bazel/bazel-at-head-plus-disabled/builds/1993#018e7e82-0fc9-4256-b3d1-68d5734333c9

- Gerrit:
https://buildkite.com/bazel/bazel-at-head-plus-disabled/builds/1993#018e7e82-816d-4cde-b1db-a5b5991e4d6e
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index bf71791..508c96c 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -150,7 +150,6 @@
         "git_repository": "https://github.com/bazelbuild/bazelisk.git",
         "file_config": ".bazelci/config.yml",
         "pipeline_slug": "bazelisk",
-        "disabled_reason": "https://github.com/bazelbuild/bazelisk/issues/558",
     },
     "Buildfarm": {
         "git_repository": "https://github.com/bazelbuild/bazel-buildfarm.git",
@@ -199,7 +198,6 @@
         "git_repository": "https://gerrit.googlesource.com/gerrit.git",
         "http_config": "https://raw.githubusercontent.com/bazelbuild/continuous-integration/master/pipelines/gerrit.yml",
         "pipeline_slug": "gerrit",
-        "disabled_reason": "https://github.com/bazelbuild/continuous-integration/issues/1881",
     },
     "Google Logging": {
         "git_repository": "https://github.com/google/glog.git",
@@ -264,7 +262,6 @@
     "rules_android": {
         "git_repository": "https://github.com/bazelbuild/rules_android.git",
         "pipeline_slug": "rules-android",
-        "disabled_reason": "https://github.com/bazelbuild/rules_android/issues/187",
     },
     "rules_android_ndk": {
         "git_repository": "https://github.com/bazelbuild/rules_android_ndk.git",