fix(amazonq): Remove setSystemCertificates from proxyUtil

[tsmithsz]

Problem

We enabled experimental proxy support in FLARE in this PR. The ProxyConfigManager within FLARE gathers and injects OS CAs. See here.

The current setSystemCertificates() call also extracts system certificates and sets NODE_EXTRA_CA_CERTS/AWS_CA_BUNDLE. This duplicates and can even override our custom logic, leading to unpredictable CA bundles.

Solution

• Remove redundant setSystemCertificates() method from proxy util.

All certificate loading now flows through a single code path (ProxyConfigManager.getCertificates()), eliminating conflicts and ensuring consistent OS CA handling.

Testing

• Tested using MITM Proxy in local capture mode

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