remove -lock and -lock-timeout for terraform init

https://www.terraform.io/upgrade-guides/0-15.html#other-minor-command-line-behavior-changes

> The -lock and -lock-timeout options are no longer available for the terraform init command. Locking applies to operations that can potentially change remote objects, to help ensure that two concurrent Terraform processes don't try to run conflicting operations, but terraform init does not interact with any providers in order to possibly effect such changes.
> These options didn't do anything in the terraform init command before, and so you can remove them from any automated calls with no change in behavior.

plugin.go

@@ -225,16 +225,6 @@ func initCommand(config InitOptions) *exec.Cmd {
 		args = append(args, fmt.Sprintf("-backend-config=%s", v))
 	}
 
-	// True is default in TF
-	if config.Lock != nil {
-		args = append(args, fmt.Sprintf("-lock=%t", *config.Lock))
-	}
-
-	// "0s" is default in TF
-	if config.LockTimeout != "" {
-		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.LockTimeout))
-	}
-
 	// Fail Terraform execution on prompt
 	args = append(args, "-input=false")