check_replace_refs: rename to read_replace_refs

This was added as a NEEDSWORK in c3c36d7de2 (replace-object:
check_replace_refs is safe in multi repo environment, 2018-04-11),
waiting for a calmer period. Since doing so now doesn't conflict
with anything in 'pu', it seems as good a time as any.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/prune.c b/builtin/prune.c
index 70ec35a..89f9d81 100644
--- a/builtin/prune.c
+++ b/builtin/prune.c
@@ -118,7 +118,7 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 
 	expire = TIME_MAX;
 	save_commit_buffer = 0;
-	check_replace_refs = 0;
+	read_replace_refs = 0;
 	ref_paranoia = 1;
 	init_revisions(&revs, prefix);