Unify OASIS_UNSAFE_SKIP_AVR_VERIFY semantics across Go and Rust attestation verification

[martintomazic]

Harmless since debug flag for testing.

On the Rust side unsafe skip verify check is minimal:

oasis-core/runtime/src/common/sgx/pcs/quote.rs

Lines 83 to 88 in 59b8f32

	if !unsafe_skip_quote_verification {
	let tcb_level = quote.verify(tcb_info, qe_identity, ts)?;
	// Validate TCB level.
	match tcb_level.status {
	TCBStatus::UpToDate | TCBStatus::SWHardeningNeeded => {}

On the go side, signature verification captures the quote verification against the policy that rust side may not ignore with unsafe skip verify set to true:

oasis-core/go/common/sgx/pcs/quote.go

Lines 196 to 200 in 59b8f32

	if !unsafeSkipVerify {
	err := q.signature.Verify(q.header, q.reportBody, ts, tcb, policy)
	if err != nil {
	return nil, err
	}