`Const` is broken

[christiangnrd]

const_arrayref calls unsafe_cached_load, which doesn't exist. We should probably fix this or just remove the code.

Metal.jl/src/device/array.jl

Lines 92 to 96 in a8e6789

	@inline function const_arrayref(A::MtlDeviceArray{T}, index::Integer) where {T}
	@boundscheck checkbounds(A, index)
	align = Base.datatype_alignment(T)
	unsafe_cached_load(pointer(A), index, Val(align))
	end

This is low priority since I don't think it's ever worked (KA's @const is not connected to this) but I opened the issue to keep track of it