Remove duplicate kubeconfig rewrite and unused crc-agent TLS helpers

Problem

cmd/crc-agent/main.go contains a map-based rewriteKubeconfigServer, while internal/resources/kubeconfig.go already provides the typed shared RewriteKubeconfigServer. The implementations differ: the agent copy silently skips malformed entries and does not clear insecure-skip-tls-verify, while the shared helper does.

cmd/crc-agent/tlsutil.go also contains unused CA, client-certificate, serving-certificate, and PEM helpers. Only TLSFromPEM is used, and it only wraps tls.X509KeyPair.

References

• cmd/crc-agent/main.go:374-403
• internal/resources/kubeconfig.go:51-68
• cmd/crc-agent/tlsutil.go:52-202
• cmd/crc-agent/clusterclient.go:72-74

Suggested direction

Use the shared kubeconfig rewrite and remove the local duplicate. Remove unused TLS helpers and private constants, or call tls.X509KeyPair directly. Preserve tests for insecure flags, file-based CA data, and empty or malformed cluster entries.

Compare cmd/crc-agent/main.go:374-403 with internal/resources/kubeconfig.go:51-68, then inspect the TLS helpers in cmd/crc-agent/tlsutil.go:52-202 and their use from cmd/crc-agent/clusterclient.go:72-74. Reuse the shared kubeconfig rewrite, remove the unused helpers or direct wrapper, and preserve coverage for insecure flags, file-based CA data, and empty or malformed cluster entries.