mount: replace mountinfo handling with moby/sys/mountinfo

Trying to reduce duplicated effort in maintaining a mountinfo
parser, this patch replaces the local implementation with the
implementation in github.com/moby/sys, which is actively maintained
and contains various optimizations.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/moby/sys/mountinfo/mountinfo_unsupported.go

@@ -0,0 +1,18 @@
+// +build !windows,!linux,!freebsd,!openbsd freebsd,!cgo openbsd,!cgo
+
+package mountinfo
+
+import (
+	"fmt"
+	"runtime"
+)
+
+var errNotImplemented = fmt.Errorf("not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+
+func parseMountTable(_ FilterFunc) ([]*Info, error) {
+	return nil, errNotImplemented
+}
+
+func mounted(path string) (bool, error) {
+	return false, errNotImplemented
+}