enable_verifier default disagrees with docs

[iximeow]

Currently we state that the verifier is disabled by default, but it is in fact enabled by default. See:

cranelift/cranelift-codegen/meta/src/shared/settings.rs

Lines 19 to 28 in afc1e0e

	settings.add_bool(
	"enable_verifier",
	r#"
	Run the Cranelift IR verifier at strategic times during compilation.
	This makes compilation slower but catches many bugs. The verifier is
	disabled by default, except when reading Cranelift IR from a text file.
	"#,
	true,
	);

This default was switched about two years ago, and has been carried forward: 774e8fc

The verifier still catches bugs IME, and it seems like a fine default, but the docs for the flag are wrong!