[cleanup] cleanup scripts/category_redirect.py
[cleanup] cleanup scripts/category_redirect.py

- use str.format(...) instead of modulo for type specifier
  arguments.
- use single quotes for string literals and double quotes **only** if
  they contain single quotes within them.
- remove preleading "u" fron strings

Change-Id: Id3103f0b118a63faeeff2ecb291a4f8314e31d1c

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core