Remove unused cert-manager/webhook scaffolding

kubebuilder's generic scaffold defensively wires up webhook TLS-cert
machinery and an unconditional cert-manager install in the e2e suite, in
case a project grows admission webhooks later. This one never will --
the spec's non-goals explicitly rule out admission webhooks and
cert-manager wiring -- so none of it does anything. Verified before
removing: no config/webhook/, no +kubebuilder:webhook markers anywhere,
and config/*/kustomization.yaml's [CERTMANAGER] blocks are all inert
(never uncommented).

cmd/main.go: drops the webhook import, the three webhook-cert-* flags,
and the WebhookServer wiring on ctrl.Options -- the manager now runs
with no webhook server, correctly, since nothing registers one. Left
the metrics-cert flags alone; those are unrelated to webhooks.

test/e2e/e2e_suite_test.go: drops the unconditional cert-manager
install/uninstall around the suite.

test/utils/utils.go: drops the now-dead InstallCertManager/
UninstallCertManager/IsCertManagerCRDsInstalled and their warnError
helper, plus UncommentCode -- unrelated to cert-manager, but found to
have zero callers even before this cleanup.

Left the inert commented-out [WEBHOOK]/[CERTMANAGER] kustomize blocks
and kubebuilder's scaffold marker comments alone: pure comments, no
runtime behavior, unlike the cert-manager install this actually removed.

Verified clean with both build tags (go build/vet, and -tags=e2e for
test/e2e). make test unchanged and green.

Co-Authored-By: Claude <noreply@anthropic.com>

.claude/settings.json

@@ -55,7 +55,8 @@
       "Bash(go doc *)",
       "Bash(go list *)",
       "Bash(gofmt -w internal/provider/config.go)",
-      "Bash(gofmt -l .)"
+      "Bash(gofmt -l .)",
+      "Bash(git restore *)"
     ],
     "additionalDirectories": [
       "/Users/jan.novak/srv/go/egress-proxies-operator/.claude",