Remove hack ignoring unused attributes for stage 0 std
Remove hack ignoring unused attributes for stage 0 std

This seems to no longer be giving spurious errors when incremental is
enabled.

aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust