We were removing the Window from TLS and thus destroying it after terminating the
windowing system, which caused an error due to calling a glfw function when it
was not inititalized.
auto merge of #1093 : larsbergstrom/servo/shutdown_window_destruction, r=metajack

We were removing the Window from TLS and thus destroying it after terminating the windowing system, which caused an error due to calling a glfw function when it was not inititalized.