CI: remove language based optimizations

We recently had a broken main branch which was not spotted, because the failing jobs did not run on it. The likely explanation is that, after merge, we are comparing main against itself, meaning nothing had changed. See how few jobs ran on this default branch pipeline: https://gitlab.com/gitlab-org/security-products/sast-rules/-/pipelines/1274435085

Slack conversation: https://gitlab.slack.com/archives/C064Q1VMM2N/p1714458794425359

To fix that, we could add another when to force execution against the default branch. But all this logic is very complex, with the list of languages repeated in so many different places.

However there are also other problems with this optimization, as in MR !559 (merged), where the required sast-rules.zip artifact to run BAP was missing, because build-and-verify did not run.

As this optimization can cause difficult to debug errors, is hard to maintain correctly, and the CPU cost savings are unclear, my recommendation is to remove it.