Remove unused WaitForDetach from Detacher interface and plugins

This has been unused since 542f2dc7, and relies on deviceName, which
can no longer be relied upon (see issue #33128).

This needs to be removed now, as part of #33128, as the code can't be
updated to attempt device detection and fallback through to the Cinder
provided deviceName, as detection "fails" when the device is gone, and
if cinder has reported a deviceName that another volume has used in
relaity, then this will block forever (or until the other, unreleated,
volume has been detached)

pkg/volume/testing/testing.go

@@ -312,7 +312,6 @@ type FakeVolume struct {
 	AttachCallCount             int
 	DetachCallCount             int
 	WaitForAttachCallCount      int
-	WaitForDetachCallCount      int
 	MountDeviceCallCount        int
 	UnmountDeviceCallCount      int
 	GetDeviceMountPathCallCount int
@@ -435,13 +434,6 @@ func (fv *FakeVolume) GetDetachCallCount() int {
 	return fv.DetachCallCount
 }
 
-func (fv *FakeVolume) WaitForDetach(devicePath string, timeout time.Duration) error {
-	fv.Lock()
-	defer fv.Unlock()
-	fv.WaitForDetachCallCount++
-	return nil
-}
-
 func (fv *FakeVolume) UnmountDevice(globalMountPath string) error {
 	fv.Lock()
 	defer fv.Unlock()