Remove unused code.

--HG--
branch : 3.1
6 jobs for topic/3.1/workbook-customDocProps in 2 minutes and 48 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #204463
test-coverage

00:01:40

95.0%
passed #204462
test-pypy3

00:00:43

passed #204458
test-python36

00:01:02

passed #204459
test-python37

00:02:47

passed #204460
test-python38

00:00:58

passed #204461
test-python39

00:00:58