Cleanup unused branches

[dblock]

Coming from opensearch-project/opensearch-clients#64, cleanup unused branches.

For some unused branches we probably want to save state, so maybe note the last revision of any branch being deleted in this issue as it's being closed.

[VachaShah]

Unused branches that can be cleaned up

backport-848-to-2.x: 6e7c240
revert-777-backport/backport-767-to-2.x: cb4e79b
backport/backport-442-to-2.x: 43bb225
backport/backport-333-to-2.x: 57cb3f6
revert-70-main: f868808

Release branches

main
2.x
2.10.3
2.10.2
2.10.1
2.10.0
2.9.1
2.8.4
2.8.3
2.8.2
2.8.1
1.x
2.0
1.0.0
0.2.1: c4f674c
0.1: 30c01a8
0.1.2: 629b827
0.2: 00e9708
0.1.1: 3456b73
0.1.x: b6b8447
former-main: 50fb70d

[VachaShah]

@dblock I think we can also clean up the 0.x.x branches which are associated with releases. WDYT?

[gaiksaya]

Deleted all unused branches mentioned above except former-main as instructed by @VachaShah. Thanks for 2PR.

[VachaShah]

Thank you @gaiksaya! I moved former-main now to the other non-deleted section. Will close this issue.

@dblock Let us know if you think there are other branches that needs to be deleted.

[dblock]

Anything unused can be deleted. Old branches from which a release was created and there's a tag that points to the same point can be deleted too.