Revert addition of conan_sources and conan_export files

What does this MR do?

This MR reverts the changes in !32866 (merged) and !32664 (merged) which allow conan_sources.tgz and conan_export.tgz files to be included in Conan package uploads.

The change worked, allowing the files to be uploaded properly, however it then prevented users from uploading packages that do not contain those files, which essentially breaks much of the existing Conan upload functionality.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related #210550 (closed)