Remove pkg/util/mount (moved out of tree)

This patch removes pkg/util/mount completely, and replaces it with the
mount package now located at k8s.io/utils/mount. The code found at
k8s.io/utils/mount was moved there from pkg/util/mount, so the code is
identical, just no longer in-tree to k/k.

pkg/cloudprovider/providers/.import-restrictions

@@ -3,20 +3,20 @@
 		{
 			"SelectorRegexp": "k8s[.]io/utils",
 			"AllowedPrefixes": [
+				"k8s.io/utils/exec",
+				"k8s.io/utils/io",
+				"k8s.io/utils/keymutex",
+				"k8s.io/utils/mount",
 				"k8s.io/utils/net",
 				"k8s.io/utils/nsenter",
-				"k8s.io/utils/io",
-				"k8s.io/utils/strings",
-				"k8s.io/utils/exec",
 				"k8s.io/utils/path",
-				"k8s.io/utils/keymutex"
+				"k8s.io/utils/strings"
 			]
 		},
 		{
 			"SelectorRegexp": "k8s[.]io/kubernetes",
 			"AllowedPrefixes": [
-				"k8s.io/kubernetes/pkg/cloudprovider/providers",
-				"k8s.io/kubernetes/pkg/util/mount"
+				"k8s.io/kubernetes/pkg/cloudprovider/providers"
 			],
 			"ForbiddenPrefixes": []
 		}