Remove references to personal debian package repo

[hughsaunders]

What does this PR do?

This dockerfile used to pull osslsigncode from a repo hosted by suse but owned by dividedmind. This is no longer required as there is now an osslsigncode package in the main debian repo. This PR removes the reference to the custom repo so the package is pulled from the main repo.

What ticket does this PR close?

Checklists

Change log

• [ ] The CHANGELOG has been updated, or
• [x] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• [ ] This PR includes new unit and integration tests to go with the code changes, or
• [x] The changes in this PR do not require tests

Documentation

• [ ] Docs (e.g. READMEs) were updated in this PR, and/or there is a follow-on issue to update docs, or
• [x] This PR does not require updating any documentation

[hughsaunders]

Could someone from @cyberark/community-and-integrations-team test this? I'm not familar enough with it to sufficiently test before merging.