tdf#97361 Make check_table.py more pythonic

Improve readability by inserting a little whitespace,
and obeying PEP 8 (python style guide) more closely.
Also remove an unused import and a few unused
local variables.

Change-Id: I07de686ec9b04e293bc4e0a092e5ad957cffbbba
Reviewed-on: https://gerrit.libreoffice.org/61624
Tested-by: Jenkins
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>