Remove the deprecated `SERVICES_API_URL` and `SERVICES_AUTH_TOKEN` constants

[aagam-shah]

Description

This PR tries to remove 2 constants as part of code cleanup for the SERVICES_AUTH_TOKEN and SERVICES_API_URL ENV variables. The site-details related token is used from the VIP_SERVICES_AUTH_TOKENS variable.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 29.57%. Comparing base (239aa5a) to head (3e99ac5). Report is 21 commits behind head on develop.

Files with missing lines	Patch %	Lines
config/class-site-details-index.php	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #5836 +/- ## ============================================= + Coverage 29.54% 29.57% +0.02% + Complexity 4782 4777 -5 ============================================= Files 282 282 Lines 20605 20585 -20 ============================================= Hits 6088 6088 + Misses 14517 14497 -20 ```

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