Clean up `stac308` UDPs and benchmarks

[soxofaan]

Once CDSE STAC migration is fully done (load_stac-based collection that is now called "SENTINEL2_L2A_STAC" is moved to "SENTINEL2_L2A", replacing the legacy opensearch once):
remove all stac308 UDPs and benchmarks that were added under #308 (for testing puproses)

FYI: to easily find all cases, I used _stac308 as suffix for UDP process ids and benchmark ids

[soxofaan]

@EmileSonneveld removed them in under #364 with

• 27861fc
• 5881215

And I did one left-over:

• 73c4f98