Cleanup knative-internal-tls secrets

[ReToCode]

Partially #14392

Proposed Changes

• Drop control-serving-certs secret, as it is unused
• Drop the routing-id label with regards to Cleanup system-internal-tls secrets and labels #14392
• Rename the comment to the new flag name

[ReToCode]

/assign @nak3
/assign @KauzClay

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.04% ⚠️

Comparison is base (45eaa1d) 86.13% compared to head (67af974) 86.09%.
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14394      +/-   ##
==========================================
- Coverage   86.13%   86.09%   -0.04%     
==========================================
  Files         196      196              
  Lines       14790    14790              
==========================================
- Hits        12739    12734       -5     
- Misses       1743     1749       +6     
+ Partials      308      307       -1     

see 6 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ReToCode]

/retest

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, ReToCode

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [dprotaso]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment