Fix CodeQL by removing unnecessary Azure SDK bootstrap

[Moary Chen (moarychan)]

Purpose

Remove the unnecessary Azure SDK source build from the samples' CodeQL workflow.

The CodeQL runs for #859 failed before scanning the samples because building Azure SDK main (7.5.0-beta.1) could not resolve maven-surefire-plugin:3.6.0 from the Azure DevOps feed (HTTP 401). The samples use released Spring Cloud Azure 7.4.0 dependencies and do not need this bootstrap.

• Remove the external SDK checkout and both SDK Maven builds.
• Preserve all pinned action SHAs, Java/JavaScript analysis, triggers, and permissions.
• Update contributor instructions to build the samples directly.

Does this introduce a breaking change?

• Yes
• No

Pull Request Type

• Bugfix
• Documentation content changes

How to Test

• YAML parsing and structural assertions pass: only the two SDK bootstrap steps are removed.
• git diff --check passes.
• Verified the unchanged sample sources with a fresh Maven repository and no locally installed SDK: mvn -f pom.xml --batch-mode --update-snapshots --no-transfer-progress -Dmaven.repo.local=<fresh-directory> -DskipTests verify passes for all 98 reactor projects on JDK 21.
• Full verify was attempted but Docker Compose tests could not connect to the local Docker daemon. No CI tests or analysis steps are disabled by this change.

What to Check

Both CodeQL matrix jobs should proceed directly to sample checkout, initialization, autobuild, and analysis without building Azure SDK main.