Revert "auto merge of #8745 : brson/rust/metadata, r=cmr"

This reverts commit 491bc3568c87dadaba4d342135bd308961c6e0ef, reversing
changes made to 05f1bbba16912f63b562a7847801823872f89ec6.
auto merge of #8751 : brson/rust/metadata-revert, r=brson

This reverts commit 491bc3568c87dadaba4d342135bd308961c6e0ef, reversing
changes made to 05f1bbba16912f63b562a7847801823872f89ec6.

I've heard reports that this broke something. Don't know details yet.