remove failing clang builds

As to beta, there are some targets that are available to build but actually fail to build in our pipelines:

1. clang freertos
2. clang zephyr (all machines)
3. clang linux seco-imx8mm-c61-*
4. all -dev images for linux-seco-px30-d23 (both clang and gcc)

The same builds that fail in our pipeline are not even run in Oniro build pipelines (clang freertos, zepyhr and seco-imx), and on the other hand no -dev images are built in Oniro pipelines (which explains why Oniro developers did not see the errors we are getting for -dev images for linux-seco-px30-d23)

We cannot leave some build jobs as manual, because the next jobs (tinfoilhat, aliens4friends) collect data from all builds; so either we keep tham (if they may be fixed) or we drop them.

For now we drop 1-2-3, while we wait for 4 to be fixed