Cranelift: Remove the old stack maps implementation

[fitzgen]

They are superseded by the new user stack maps implementation.

[elliottt]

Awesome!

[bjorn3]

Can cranelift-tool print user stackmaps?

[fitzgen]

The vcode's debug implementation should include the stack maps:

wasmtime/cranelift/filetests/filetests/isa/x64/user_stack_maps.clif

Lines 55 to 68 in 9d35545

	; call User(userextname0)
	; ; UserStackMap { by_type: [(types::I32, CompoundBitSet {0, 4, 8})], sp_to_sized_stack_slots: None }
	; lea rsp(0 + virtual offset), %rcx
	; movl $1, 0(%rcx)
	; lea rsp(4 + virtual offset), %rdx
	; movl $2, 0(%rdx)
	; movq %r15, %rdi
	; call User(userextname0)
	; ; UserStackMap { by_type: [(types::I32, CompoundBitSet {0, 4})], sp_to_sized_stack_slots: None }
	; lea rsp(0 + virtual offset), %r9
	; movl $2, 0(%r9)
	; movq %rbx, %rdi
	; call User(userextname0)
	; ; UserStackMap { by_type: [(types::I32, CompoundBitSet {0})], sp_to_sized_stack_slots: None }