posix: remove the is_temp things that prevented use-after-frees

https://github.com/odin-lang/Odin/commit/d0709a7de21efded4625167dbff4a7dd13d561b4
fixes those another way.

core/os/os2/env_windows.odin

@@ -8,7 +8,7 @@ _lookup_env :: proc(key: string, allocator: runtime.Allocator) -> (value: string
 	if key == "" {
 		return
 	}
-	TEMP_ALLOCATOR_GUARD(ignore=is_temp(allocator))
+	TEMP_ALLOCATOR_GUARD()
 	wkey, _ := win32_utf8_to_wstring(key, temp_allocator())
 
 	n := win32.GetEnvironmentVariableW(wkey, nil, 0)