Remove unused code from target_listener module

[vandrijevik]

Our code in chef-repo never specifies a value for the variable create_listener, so this variable always gets the default value true in the module’s code.

This PR removes the unused variable, along with all the code that is unused as a result of its removal.

My goal is to simplify the code in this repository related to application load balancers, so that we can create a fully-functiona load balancer with one module declaration, instead of the three that we use today. This is the first step towards that goal.

The diff in the planshot is due to AWS changing their API response, which is why enable_cross_zone_load_balancing is gone as an attribute — per this issue and AWS’s documentation:

With Application Load Balancers, cross-zone load balancing is always enabled.

[vandrijevik]

As proof that this doesn’t change anything for an application load balancer in chef-repo which uses the module, the following diff, which updates usage of this module to the code in this branch, yields an empty plan:

-  source = "github.com/tablexi/terraform_modules?ref=7ae7189//aws/ec2/load_balancers/lb"
+  source = "github.com/tablexi/terraform_modules?ref=d77dddc//aws/ec2/load_balancers/lb"