rt: Remove useless libuv wrappers. #5429

This removes almost all of the simple wrappers from rust_uv.cpp.
For some reason uv_getaddrinfo and uv_freeaddrinfo still can't be removed.
auto merge of #6196 : brson/rust/uvwrappers, r=brson

This removes almost all of the simple wrappers from rust_uv.cpp.
For some reason uv_getaddrinfo and uv_freeaddrinfo still can't be removed.