Merge branch 'ps/reftable-drop-generic'

Merge branch 'ps/reftable-drop-generic'

The code in the reftable library has been cleaned up by discarding
unused "generic" interface.

* ps/reftable-drop-generic:
  reftable: mark unused parameters in empty iterator functions
  reftable/generic: drop interface
  t/helper: refactor to not use `struct reftable_table`
  t/helper: use `hash_to_hex_algop()` to print hashes
  t/helper: inline printing of reftable records
  t/helper: inline `reftable_table_print()`
  t/helper: inline `reftable_stack_print_directory()`
  t/helper: inline `reftable_reader_print_file()`
  t/helper: inline `reftable_dump_main()`
  reftable/dump: drop unused `compact_stack()`
  reftable/generic: move generic iterator code into iterator interface
  reftable/iter: drop double-checking logic
  reftable/stack: open-code reading refs
  reftable/merged: stop using generic tables in the merged table
  reftable/merged: rename `reftable_new_merged_table()`
  reftable/merged: expose functions to initialize iterators