os: skip TestRemoveAllRace on Windows
os: skip TestRemoveAllRace on Windows

It's just fundamentally incompatible with
Windows' pickiness about removing things
that are in use.

TBR=brainman
CC=golang-codereviews
https://codereview.appspot.com/142270043

bryanxu/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,d0f/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,d0f/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,bryanxu/go-zh,bryanxu/go-zh