Remove unnecessary and over-restrictive type check in SystemRandom.getrandbits()

[rhettinger]

• The type check is over-restrictive (i.e. doesn't allow int subclasses).
• The type check is unnecessary:
  • We already that know k can be compared to 0
  • In the subsequent step, urandom() verifies that (k + 7) // 8 is an instance of integer, and if not will raise a TypeError for us.
• The code is performance sensitive (called in the inner loops for shuffle(), sample(), and choices()).

[vstinner]

LGTM.

I confirm that os.urandom(float) raises a TypeError. I also checked and test_random already ensures that getrandbits(float) raises a TypeError, so this change LGTM.

nitpick: you might just try to write a shorter title for the commit when you merge your change :-)