[Pages] Remove deprecated `useHttp2` parameter
Summary
Context: !2270 (comment 747493200)
... we deprecated this parameter: https://gitlab.com/gitlab-org/gitlab-pages/blob/f9d008b7e62b92d8843b0cb6a6a3ac46c338e456/internal/config/flags.go#L15-L15
Acceptance criteria
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Deprecated parameter is removed from Charts configuration
Edited by Jason Plum