integration-cli: remove unused requirements utils

Removes some test functions that were unused:

- bridgeNfIP6tables
- ambientCapabilities (added to support #26979, which was reverted in #27737)
- overlay2Supported

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

integration-cli/requirements_unix_test.go

@@ -84,20 +84,11 @@ func bridgeNfIptables() bool {
 	return !SysInfo.BridgeNFCallIPTablesDisabled
 }
 
-func bridgeNfIP6tables() bool {
-	return !SysInfo.BridgeNFCallIP6TablesDisabled
-}
-
 func unprivilegedUsernsClone() bool {
 	content, err := ioutil.ReadFile("/proc/sys/kernel/unprivileged_userns_clone")
 	return err != nil || !strings.Contains(string(content), "0")
 }
 
-func ambientCapabilities() bool {
-	content, err := ioutil.ReadFile("/proc/self/status")
-	return err != nil || strings.Contains(string(content), "CapAmb:")
-}
-
 func overlayFSSupported() bool {
 	cmd := exec.Command(dockerBinary, "run", "--rm", "busybox", "/bin/sh", "-c", "cat /proc/filesystems")
 	out, err := cmd.CombinedOutput()
@@ -107,20 +98,6 @@ func overlayFSSupported() bool {
 	return bytes.Contains(out, []byte("overlay\n"))
 }
 
-func overlay2Supported() bool {
-	if !overlayFSSupported() {
-		return false
-	}
-
-	daemonV, err := kernel.ParseRelease(testEnv.DaemonInfo.KernelVersion)
-	if err != nil {
-		return false
-	}
-	requiredV := kernel.VersionInfo{Kernel: 4}
-	return kernel.CompareKernelVersion(*daemonV, requiredV) > -1
-
-}
-
 func init() {
 	if testEnv.IsLocalDaemon() {
 		SysInfo = sysinfo.New(true)