fix: remove unreachable product fetch block

[anujk14]

Per documentation, the entitlement check should work with both, product id as well as feature id.
However, this is what the actual behaviour is:

1. We try to fetch the feature by feature id
2. In case there is no feature, we return an error
3. Thus, even if someone tries to check entitlement with product id, they would never be able to do so since we would never reach the product block once feature check fails.

This PR updates the method to work with only feature IDs, as that is what the existing behaviour is.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
frontier	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 30, 2024 8:58am

[coveralls]

Pull Request Test Coverage Report for Build 10629829768

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 23 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 9.505%

---

Files with Coverage Reduction	New Missed Lines	%
billing/entitlement/mocks/product_service.go	23	46.28%

Totals
Change from base Build 10628472009:	-0.02%
Covered Lines:	10524
Relevant Lines:	110716

---

💛 - Coveralls