chore: Remove pre-Python 3.9 code #793

Job	Run time
Test machine readable to human-readable date/time using Nix	36s
Test Sentinel-1 using Nix	50s
Lint content	1m 44s
Test Sentinel-2 using Nix	1m 7s
Test Sentinel-1 on macos-12, using Poetry with Python 3.9	4m 30s
Test Sentinel-2 on macos-12, using Poetry with Python 3.9	6m 34s
Test Sentinel-1 on macos-12, using Poetry with Python 3.11	3m 53s
Test Sentinel-2 on macos-12, using Poetry with Python 3.11	9m 46s
Test Sentinel-1 on ubuntu-22.04, using Poetry with Python 3.9	1m 35s
Test Sentinel-2 on ubuntu-22.04, using Poetry with Python 3.9	1m 54s
Test Sentinel-1 on ubuntu-22.04, using Poetry with Python 3.11	1m 16s
Test Sentinel-2 on ubuntu-22.04, using Poetry with Python 3.11	6m 57s
Test Sentinel-1 on windows-2022, using Poetry with Python 3.9	5m 39s
Test Sentinel-2 on windows-2022, using Poetry with Python 3.9	10m 21s
Test Sentinel-1 on windows-2022, using Poetry with Python 3.11	5m 34s
Test Sentinel-2 on windows-2022, using Poetry with Python 3.11	14m 24s
finalise	1s
	1h 16m 41s

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