Remove all buildkite references (#1444)

What changed?
Remove all deprecated references to buildkite.

Why?
Because we are migrating to only use Github Actions.

How did you test it?
I am testing using the Github Actions pipeline.

Potential risks
Removing it could make it so that a push/PR passes when it shouldn't (because the Github Actions failed to catch it).
---------

Co-authored-by: Mandy Chen <mandy.chen@uber.com>
Co-authored-by: Shijie Sheng <shengs@uber.com>

Author: 3 people

.buildkite/pipeline.yml

@@ -21,7 +21,12 @@ jobs:
           go-version: '1.23.4'
 
       - name: Run unit test
-        run: docker compose -f docker/github_actions/docker-compose.yml run unit-test bash -c "make unit_test && ./scripts/gen_coverage_metadata.sh .build/metadata.txt"
+        uses: nick-fields/retry@v3
+        with:
+          max_attempts: 2
+          timeout_minutes: 30
+          command: |
+            docker compose -f docker/github_actions/docker-compose.yml run unit-test bash -c "make unit_test && ./scripts/gen_coverage_metadata.sh .build/metadata.txt"
 
       - name: Upload coverage artifacts
         if: always()

.buildkite/scripts/fossa.sh

@@ -1,5 +1,5 @@
 # Go framework for Cadence
-[![Build Status](https://badge.buildkite.com/e7241785444519bdfd1defc68839fd19a89c15adb3477c73f7.svg?theme=github&branch=master)](https://buildkite.com/uberopensource/cadence-go-client)
+[![CI Checks](https://github.com/cadence-workflow/cadence-go-client/actions/workflows/ci-checks.yml/badge.svg)](https://github.com/cadence-workflow/cadence-go-client/actions/workflows/ci-checks.yml)
 [![Coverage](https://codecov.io/gh/uber-go/cadence-client/graph/badge.svg?token=iEpqo5HbDe)](https://codecov.io/gh/uber-go/cadence-client)
 [![GoDoc](https://godoc.org/go.uber.org/cadence?status.svg)](https://godoc.org/go.uber.org/cadence)