On the 'move-tracking-2' branch: Remove 'branch family' and 'branch sibling definition' data types.
The 'family' concept has been redundant since r1673476. The 'sibling' concept, that is the concept of groups of branches having something in common, is not currently used, and so was just confusing.
No behavioural change.
* subversion/include/private/svn_branch.h (svn_branch_family_t, svn_branch_sibling_t): Delete. (svn_branch_revision_root_t): Move the first and next EID fields to here. (svn_branch_instance_t): Move the root EID field to here. Elsewhere: adjust accordingly.