parameter field_name not required for tc.build_type_api.change_requirement_setting

Hi,

As seen here: [build_type_api.change_requirement_setting](https://devopshq.github.io/teamcity/swagger/api/BuildTypeApi.html#change-requirement-setting)
this function requires an parameter field_name, which must not be used at all for the function. All values for it other than `""` (empty str) leads to an error, as the parameter is currently mandatory by validation, but must be always `""` to build the correct url for the underlying TC RestAPI call.

To use this function at it's current state, it needs to be called as (using dohq-teamcity Types below):

```
bt: BuildType
ar: AgentRequirement

api_response = tc.build_type_api.change_requirement_setting(bt, ar, "", body=ar)

```

The parameter should be removed.

Thanks and Cheers
--- mnse

Start at tc.build_type_api.change_requirement_setting and compare its current signature and validation with the linked BuildTypeApi documentation. The change is done when callers no longer need to provide field_name and the underlying TeamCity REST API URL is still built correctly.

Written by the indexing model from the issue text.