operator: drop replace github.com/cyphar/filepath-securejoin

[joejulian]

To address a synk finding, the version of github.com/cyphar/filepath-securejoin was bumped to v0.2.4 with a replace (#13354). Once we can upgrade fluxcd (blocked by fluxcd/helm-controller#699), we should remove this replace:

go mod edit -dropreplace github.com/cyphar/filepath-securejoin

JIRA Link: CORE-1437