lib/osutil: Disable setting priority on Windows (fixes #4676)

Presumably fixing the crash, leaving us to improve this calmly.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4677

lib/osutil/lowprio_windows.go

@@ -6,42 +6,8 @@
 
 package osutil
 
-import (
-	"syscall"
-
-	"github.com/pkg/errors"
-)
-
-var (
-	kernel32, _         = syscall.LoadLibrary("kernel32.dll")
-	setPriorityClass, _ = syscall.GetProcAddress(kernel32, "SetPriorityClass")
-)
-
-const (
-	// https://msdn.microsoft.com/en-us/library/windows/desktop/ms686219(v=vs.85).aspx
-	aboveNormalPriorityClass   = 0x00008000
-	belowNormalPriorityClass   = 0x00004000
-	highPriorityClass          = 0x00000080
-	idlePriorityClass          = 0x00000040
-	normalPriorityClass        = 0x00000020
-	processModeBackgroundBegin = 0x00100000
-	processModeBackgroundEnd   = 0x00200000
-	realtimePriorityClass      = 0x00000100
-)
-
 // SetLowPriority lowers the process CPU scheduling priority, and possibly
 // I/O priority depending on the platform and OS.
 func SetLowPriority() error {
-	handle, err := syscall.GetCurrentProcess()
-	if err != nil {
-		return errors.Wrap(err, "get process handler")
-	}
-	defer syscall.CloseHandle(handle)
-
-	res, _, err := syscall.Syscall(uintptr(setPriorityClass), uintptr(handle), belowNormalPriorityClass, 0, 0)
-	if res != 0 {
-		// "If the function succeeds, the return value is nonzero."
 	return nil
 }
-	return errors.Wrap(err, "set priority class") // wraps nil as nil
-}