Merge branch 'ab/read-tree'

Merge branch 'ab/read-tree'

Code simplification by removing support for a caller that is long gone.

* ab/read-tree:
  tree.h API: simplify read_tree_recursive() signature
  tree.h API: expose read_tree_1() as read_tree_at()
  archive: stop passing "stage" through read_tree_recursive()
  ls-files: refactor away read_tree()
  ls-files: don't needlessly pass around stage variable
  tree.c API: move read_tree() into builtin/ls-files.c
  ls-files tests: add meaningful --with-tree tests
  show tests: add test for "git show <tree>"