chore: closes #496 (#499)

Since the CI configuration in the test folder is no longer needed, we can safely delete those.

test/ci/beta-cluster.yml

----
-
-platform: linux
-
-inputs:
-- name: pull-request
-  path: terraform-google-kubernetes-engine
-
-run:
-  path: make
-  args: ['test_integration']
-  dir: terraform-google-kubernetes-engine
-
-params:
-  SUITE: "beta-cluster-local"
-  COMPUTE_ENGINE_SERVICE_ACCOUNT: ""
-  REGION: "us-east4"
-  ZONES: '["us-east4-a", "us-east4-b", "us-east4-c"]'

test/ci/private-zonal-with-networking.yml

----
-
-platform: linux
-
-inputs:
-- name: pull-request
-  path: terraform-google-kubernetes-engine
-
-run:
-  path: make
-  args: ['test_integration']
-  dir: terraform-google-kubernetes-engine
-
-params:
-  SUITE: "private-zonal-with-networking-local"
-  COMPUTE_ENGINE_SERVICE_ACCOUNT: ""
-  REGION: "us-east4"
-  ZONES: '["us-east4-a", "us-east4-b", "us-east4-c"]'

test/ci/safer-cluster.yml

----
-
-platform: linux
-
-inputs:
-- name: pull-request
-  path: terraform-google-kubernetes-engine
-
-run:
-  path: make
-  args: ['test_integration']
-  dir: terraform-google-kubernetes-engine
-
-params:
-  SUITE: "safer-cluster-local"
-  COMPUTE_ENGINE_SERVICE_ACCOUNT: ""
-  REGION: "us-east4"
-  ZONES: '["us-east4-a", "us-east4-b", "us-east4-c"]'

test/ci/simple-regional-with-networking.yml

----
-
-platform: linux
-
-inputs:
-- name: pull-request
-  path: terraform-google-kubernetes-engine
-
-run:
-  path: make
-  args: ['test_integration']
-  dir: terraform-google-kubernetes-engine
-
-params:
-  SUITE: "simple-regional-with-networking-local"
-  COMPUTE_ENGINE_SERVICE_ACCOUNT: ""
-  REGION: "us-east4"
-  ZONES: '["us-east4-a", "us-east4-b", "us-east4-c"]'