Merge branch 'ps/reftable-write-optim'

Code to write out reftable has seen some optimization and
simplification.

* ps/reftable-write-optim:
  reftable/block: reuse compressed array
  reftable/block: reuse zstream when writing log blocks
  reftable/writer: reset `last_key` instead of releasing it
  reftable/writer: unify releasing memory
  reftable/writer: refactorings for `writer_flush_nonempty_block()`
  reftable/writer: refactorings for `writer_add_record()`
  refs/reftable: don't recompute committer ident
  reftable: remove name checks
  refs/reftable: skip duplicate name checks
  refs/reftable: perform explicit D/F check when writing symrefs
  refs/reftable: fix D/F conflict error message on ref copy

reftable/reftable-error.h

@@ -48,9 +48,6 @@ enum reftable_error {
 	/* Wrote a table without blocks. */
 	REFTABLE_EMPTY_TABLE_ERROR = -8,
 
-	/* Dir/file conflict. */
-	REFTABLE_NAME_CONFLICT = -9,
-
 	/* Invalid ref name. */
 	REFTABLE_REFNAME_ERROR = -10,