Secure Test Projects - Remove SAST / SAST QA

As per #366852 (closed) - SAST uses it's own tests at analyzer level rather than downstream repos.

With recent SAST changes we're seeing Secure Test project failures due to requiring SAST templates that no longer exist:

php-composer-master - gitlab-org/security-products/tests/php-composer!67 (merged)
ruby-bundler-rails-offline-FREEZE - gitlab-org/security-products/tests/ruby-bundler-rails!57 (merged)
ruby-bundler-rails-master - gitlab-org/security-products/tests/ruby-bundler-rails!56 (merged)
c-offline-FREEZE - gitlab-org/security-products/tests/c!26 (merged)
cplusplus-offline-FREEZE - gitlab-org/security-products/tests/cplusplus!18 (merged)
cplusplus-master - gitlab-org/security-products/tests/cplusplus!17 (merged)
nodejs-master - gitlab-org/security-products/tests/nodejs!8 (merged)
java-android-master - gitlab-org/security-products/tests/java-android!18 (merged)
dotnet5-master - gitlab-org/security-products/tests/dotnet5!6 (merged) - gitlab-org/security-products/tests/dotnet5!7 (merged)
ruby-generic-master - gitlab-org/security-products/tests/ruby-generic!2 (merged)

Either:

• Remove SAST entirely (CI and README)
• Or remove SAST QA job, proving out that SAST at least runs successfully