refactor: Remove old InsecureSecrets backward compatibility elements

[lenny-goodell]

Old elements were left in-place until all Device/App services got updated with the latest go-mod-bootstrap, which happened with the 3.0 release.

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/edgex-go/blob/main/.github/Contributing.md

PR Checklist

Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?) N/A
• I have fully tested (add details below) this the new feature or bug fix (if not, why?) N/A
• I have opened a PR for the related docs change (if not, why?) N/A

Testing Instructions

New Dependency Instructions (If applicable)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[ejlee3]

LGTM

[codecov-commenter]

Codecov Report

Merging #4672 (bec9b59) into main (488f23b) will not change coverage.
The diff coverage is n/a.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the GitHub App Integration for your organization. Read more.

@@           Coverage Diff           @@
##             main    #4672   +/-   ##
=======================================
  Coverage   41.84%   41.84%           
=======================================
  Files         105      105           
  Lines        9723     9723           
=======================================
  Hits         4069     4069           
  Misses       5308     5308           
  Partials      346      346