Remove architecture from repository names

[AMDmi3]

E.g. Void Linux x86_64 and OpenWrt 19.07 x86_64 should not contain arch in their name as we do not differentiate repositories by arch (there should be other mechanism to explore arch related differences). This requires renaming internal repository id (void_x86_64), which is also used in other Repology places:

• [ ] packages (repo) (trivial update)
• [ ] repositories (name) (trivial update)
• [ ] metapackages_events (data->'repos', data->'all_repos', data->'repos_added', data->'last_repos', data->'repos_removed')
• [ ] metapackages (devel_repos, newest_repos, all_repos) (should go away when events generation is rewritten)
• [ ] problems (trivial update or regenerate)
• [ ] repositories_history (hash keys) (see #999)

It's a nice chance to switch more places to repository id numbers for more efficient storage and avoiding problems like this in future.

[AMDmi3]

XXX: while here, also rename openmandriva_4 to openmandriva_4_0 (#1010)