Add typing to scrapy/utils/gz.py and remove dead code.

scrapy/utils/gz.py

@@ -1,15 +1,18 @@
 import struct
 from gzip import GzipFile
 from io import BytesIO
+from typing import List
+
+from scrapy.http import Response
 
 
-def gunzip(data):
+def gunzip(data: bytes) -> bytes:
     """Gunzip the given data and return as much data as possible.
 
     This is resilient to CRC checksum errors.
     """
     f = GzipFile(fileobj=BytesIO(data))
-    output_list = []
+    output_list: List[bytes] = []
     chunk = b"."
     while chunk:
         try:
@@ -18,17 +21,13 @@ def gunzip(data):
         except (IOError, EOFError, struct.error):
             # complete only if there is some data, otherwise re-raise
             # see issue 87 about catching struct.error
-            # some pages are quite small so output_list is empty and f.extrabuf
-            # contains the whole page content
-            if output_list or getattr(f, "extrabuf", None):
-                try:
-                    output_list.append(f.extrabuf[-f.extrasize :])
-                finally:
-                    break
+            # some pages are quite small so output_list is empty
+            if output_list:
+                break
             else:
                 raise
     return b"".join(output_list)
 
 
-def gzip_magic_number(response):
+def gzip_magic_number(response: Response) -> bool:
     return response.body[:3] == b"\x1f\x8b\x08"