sha1-file: fix outdated sha1 comment references

Commit 17e65451e3 (sha1_file: convert check_sha1_signature to struct
object_id, 2018-03-12) switched to using the name "oid", but forgot to
update the variable name in the comment.

Likewise, b4f5aca40e (sha1_file: convert read_sha1_file to struct
object_id, 2018-03-12) dropped the name read_sha1_file(), but missed a
comment which mentions it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1-file.c

@@ -124,7 +124,7 @@ const char *empty_blob_oid_hex(void)
 
 /*
  * This is meant to hold a *small* number of objects that you would
- * want read_sha1_file() to be able to return, but yet you do not want
+ * want read_object_file() to be able to return, but yet you do not want
  * to write them into the object store (e.g. a browse-only
  * application).
  */
@@ -798,8 +798,8 @@ void *xmmap(void *start, size_t length,
 
 /*
  * With an in-core object data in "map", rehash it to make sure the
- * object name actually matches "sha1" to detect object corruption.
- * With "map" == NULL, try reading the object named with "sha1" using
+ * object name actually matches "oid" to detect object corruption.
+ * With "map" == NULL, try reading the object named with "oid" using
  * the streaming interface and rehash it to do the same.
  */
 int check_object_signature(const struct object_id *oid, void *map,