`make check-stage1-doc-ref` is broken

[catamorphism]

The following commands no longer seem to work:

make check-stage1-doc-tutorial
make check-stage1-doc-ref
make check-stage2-doc-tutorial
make check-stage2-doc-ref

With incoming, I just get make: *** No rule to make target check-stage2-doc-tutorial'. Stop.` and so on.

[graydon]

Note: the pull request I just filed fixes the check-stage2-doc-$doc targets, but the manual target is check-stage2-doc-rust, not check-stage2-doc-ref as you've written in the bug here. I think if the latter used to work, it's stopped working as-intended. The document name is rust.md after all.

[catamorphism]

I got the names from https://github.com/mozilla/rust/wiki/Note-testsuite

[brson]

Sorry, that was fallout from reorganization of tests.mk.

[graydon]

adjusted wiki page