CI: Remove Flatcar specifics

We don't test Flatcar at all in CI, thus remove special handling for it.

tests/testcases/015_check-nodes-ready.yml

@@ -1,18 +1,10 @@
 ---
 - name: Testcases checking nodes
   hosts: kube_control_plane[0]
+  vars:
+    bin_dir: /usr/local/bin
   tasks:
 
-  - name: Force binaries directory for Flatcar Container Linux by Kinvolk
-    set_fact:
-      bin_dir: "/opt/bin"
-    when: ansible_os_family in ["Flatcar", "Flatcar Container Linux by Kinvolk"]
-
-  - name: Force binaries directory for other hosts
-    set_fact:
-      bin_dir: "/usr/local/bin"
-    when: not ansible_os_family in ["Flatcar", "Flatcar Container Linux by Kinvolk"]
-
   - import_role:  # noqa name[missing]
       name: cluster-dump