replace "dep" with "go mod"

A simple "go mod init && go mod tidy && go mod vendor" was enough and
mostly seems to have picked the same revisions of the dependencies as
before. Notable exceptions are klog and gogo/protobuf.

vendor/golang.org/x/sys/unix/mksysnum.go

@@ -139,7 +139,7 @@ func main() {
 				text += format(name, num, proto)
 			}
 		case "freebsd":
-			if t.Match(`^([0-9]+)\s+\S+\s+(?:NO)?STD\s+({ \S+\s+(\w+).*)$`) {
+			if t.Match(`^([0-9]+)\s+\S+\s+(?:(?:NO)?STD|COMPAT10)\s+({ \S+\s+(\w+).*)$`) {
 				num, proto := t.sub[1], t.sub[2]
 				name := fmt.Sprintf("SYS_%s", t.sub[3])
 				text += format(name, num, proto)