Remove all references for dropped OVALs

[yuumasato]

Description:

• Remove all references to OVAL definitions dropped due to incompleteness.

Rationale:

• OVAL 5.10 doesn't have systemdunitproperty test, and some definitions can be incomplete.
• When building content with only OVAL 5.10, incomplete OVAL definitions are dropped. But references to these definitions still existed in auxiliary data structures. Not dropping them was causing a traceback when later we tried to add check-exports.

Traceback (most recent call last):
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/utils/relabel-ids.py", line 514, in <module>
    main()
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/utils/relabel-ids.py", line 500, in main
    oval_linker.link_xccdf()
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/utils/relabel-ids.py", line 99, in link_xccdf
    self.add_missing_check_exports(check, checkcontentref)
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/utils/relabel-ids.py", line 225, in add_missing_check_exports
    for def_id in self.get_nested_definitions(check_name):
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/utils/relabel-ids.py", line 211, in get_nested_definitions
    extensions = parse_oval.find_extending_defs(self.oval_groups, definition_tree)
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/modules/parse_oval.py", line 94, in find_extending_defs
    finder.find_element(defn, "extend_definition", "definition_ref")
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/modules/parse_oval.py", line 35, in find_element
    self._recurse(start_element)
  File "/home/jenkins/workspace/scap-security-guide-nightly-oval510-zip/shared/modules/parse_oval.py", line 38, in _recurse
    if element.tag.endswith(self.target):
AttributeError: 'NoneType' object has no attribute 'tag'

[pep8speaks]

Hello @yuumasato! Thanks for submitting the PR.

• In the file shared/utils/relabel-ids.py, following are the PEP8 issues :

Line 14:1: E402 module level import not at top of file
Line 15:1: E402 module level import not at top of file
Line 20:1: E402 module level import not at top of file

[yuumasato]

For reference Jenkins trying to build content with only OVAL 5.10: https://jenkins.open-scap.org/view/SCAP%20Security%20Guide/job/scap-security-guide-nightly-oval510-zip/

[mpreisler]

ACK