Remove dl.google.com repository from Linux packages

[fmarier]

This disables the cronjob that gets installed by the RPM and DEB packages in
order to forcefully add (or re-add) the Google Chrome package repository and
signing key.

This fixes brave/brave-browser#1084 and fixes brave/brave-browser#1967.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone

Test Plan:

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

[fmarier]

@mbacchi This is the same pull request you've already reviewed at #1078 but for dev/0.61.x.

[mbacchi]

Looks good!