[clang-format][NFC] Use prog in clang-format-diff.py (#74399)

This is a minor improvement to #73491.

Author: owenca

clang/tools/clang-format/clang-format-diff.py

@@ -25,7 +25,6 @@
 
 import argparse
 import difflib
-import os
 import re
 import subprocess
 import sys
@@ -37,9 +36,8 @@
 
 
 def main():
-    basename = os.path.basename(sys.argv[0])
     parser = argparse.ArgumentParser(
-        description=__doc__.format(clang_format_diff=basename),
+        description=__doc__.format(clang_format_diff="%(prog)s"),
         formatter_class=argparse.RawDescriptionHelpFormatter,
     )
     parser.add_argument(