Drop OBJ_VERSION_NO_HEADER_AAD (pack object format v1) support before rc1

[mr-raj12]

Title: Drop OBJ_VERSION_NO_HEADER_AAD (pack object format v1) support before rc1

Body:
RepoObj.parse() and parse_meta() accept two pack object format versions right now: OBJ_VERSION_NO_HEADER_AAD (0x01) and OBJ_VERSION_HEADER_AAD (0x02). We only write 0x02; 0x01 is kept so objects from older borg2 betas still read back fine.

We don't owe compatibility across beta versions, so this fallback has no real reason to exist once we're past the current round of betas. Leaving it in after that is just dead weight: an extra branch and an extra accepted version number for nobody.

Before rc1: drop OBJ_VERSION_NO_HEADER_AAD from SUPPORTED_OBJ_VERSIONS in src/borg/repoobj.py, remove the version-0x01 branches in parse()/parse_meta(), and remove test_version1_object_without_header_aad_still_readable in src/borg/testsuite/repoobj_test.py.

Reference: #9946

[ThomasWaldmann]

Note: 0x01 is only used by beta 22 (before there were no packs, b23 will have 0x02).