Remove header policy tests from public QUICHE.
Remove header policy tests from public QUICHE.

Remove BalsaHeadersTest.GfeHeaderPolicyGfeBug and
GfeHeaderPolicyExemptionNoGfeBug from public QUICHE, as default
QuicheHandleHeaderPolicyImpl() (provided in
quiche/common/platform/default/quiche_platform_impl/quiche_header_policy_impl.h)
is a no-op.

PiperOrigin-RevId: 446015684

google/quiche,google/quiche,google/quiche,google/quiche