Remove workaround to perf issues in go1.6

Starting in go1.9, Golang lowers the timer frequency when not required
reducing CPU usage. This workaround prevents Golang from doing so,
and since the initial issue was fixed, I see no perf regressions.
This does not need to be conditional based on Golang verison, as the issue
being worked around was only in go1.6.

Signed-off-by: Darren Stahl <darst@microsoft.com>

zsyscall_windows.go

@@ -38,14 +38,12 @@ func errnoErr(e syscall.Errno) error {
 
 var (
 	modkernel32 = windows.NewLazySystemDLL("kernel32.dll")
-	modwinmm    = windows.NewLazySystemDLL("winmm.dll")
 	modadvapi32 = windows.NewLazySystemDLL("advapi32.dll")
 
 	procCancelIoEx                                           = modkernel32.NewProc("CancelIoEx")
 	procCreateIoCompletionPort                               = modkernel32.NewProc("CreateIoCompletionPort")
 	procGetQueuedCompletionStatus                            = modkernel32.NewProc("GetQueuedCompletionStatus")
 	procSetFileCompletionNotificationModes                   = modkernel32.NewProc("SetFileCompletionNotificationModes")
-	proctimeBeginPeriod                                      = modwinmm.NewProc("timeBeginPeriod")
 	procConnectNamedPipe                                     = modkernel32.NewProc("ConnectNamedPipe")
 	procCreateNamedPipeW                                     = modkernel32.NewProc("CreateNamedPipeW")
 	procCreateFileW                                          = modkernel32.NewProc("CreateFileW")
@@ -122,12 +120,6 @@ func setFileCompletionNotificationModes(h syscall.Handle, flags uint8) (err erro
 	return
 }
 
-func timeBeginPeriod(period uint32) (n int32) {
-	r0, _, _ := syscall.Syscall(proctimeBeginPeriod.Addr(), 1, uintptr(period), 0, 0)
-	n = int32(r0)
-	return
-}
-
 func connectNamedPipe(pipe syscall.Handle, o *syscall.Overlapped) (err error) {
 	r1, _, e1 := syscall.Syscall(procConnectNamedPipe.Addr(), 2, uintptr(pipe), uintptr(unsafe.Pointer(o)), 0)
 	if r1 == 0 {