rt: Remove rust_env
Remove the annihilate lang item
rt: Remove rust_signal.h
rt: Remove unused parts of rust_globals.h
rt: Remove unused parts of rust_log
rt: Remove rust_refcount.h
rt: Remove rust_stack
rt: Remove unused rust_clone_type_desc declaration
rt: Remove empty rust_upcall.h
rt: Remove unused uv helpers
auto merge of #8433 : brson/rust/rm-more-oldrt-crud, r=brson

Just deleting more stuff.