build: Remove workaround for hatchling upgrades

[jku]

Apparently Dependabot now supports upgrading build-system.requires: we don't need the workarounds anymore.

Looks like it works:

updater | 2025/02/21 08:02:36 INFO <job_968450357> Checking if hatchling 1.27.0 needs updating
  proxy | 2025/02/21 08:02:36 [021] GET https://pypi.org:443/simple/hatchling/
  proxy | 2025/02/21 08:02:36 [021] 200 https://pypi.org:443/simple/hatchling/
updater | 2025/02/21 08:02:36 INFO <job_968450357> Filtered out 14 yanked versions
updater | 2025/02/21 08:02:36 INFO <job_968450357> Latest version is 1.27.0