mirrors.yml: various updates
- remove `tencent` mirror, sync discontinued by downstream
- remove `koddos-hk`, sync discontinued by downstream
- add `repo-us`, AOSC's repository mirror in US
- add `bfsu4` and `bfsu6`, BFSU's v4/v6 only domain
- add `pku`, Peking University's Mirror
- add `qlut`, Qilu University of Technology's Mirror
- add `cernet`, CERNET mirrors' redirection service with IP-based optimization
- use https for `tsukuba` and `jlu` mirror
- declare `xtom` mirror's location in US
- add /anthon/ suffix for `origin`, `origin4`, `origin6` and `fastly`
- fix some typo
