test: Remove most uses of `&fn()` from the tests.
librustc: Remove remaining uses of `&fn()` in favor of `||`.
libsyntax: Remove the old-style borrowed closure type syntax from the
language.
libstd: Remove all non-`proc` uses of `do` from libstd
auto merge of #10581 : pcwalton/rust/dedo, r=alexcrichton

r? @alexcrichton