remove commented out code

Author: hjwp

tests/book_tester.py

@@ -315,10 +315,7 @@ def parse_listings(self):
     def check_final_diff(self, ignore=None, diff=None):
         if diff is None:
             diff = self.run_command(Command(f"git diff -w repo/{self.chapter_name}"))
-        # try:
         print("checking final diff", diff)
-        # except io.BlockingIOError:
-        # pass
         self.assertNotIn("fatal:", diff)
         start_marker = "diff --git a/\n"
         commit = Commit.from_diff(start_marker + diff)