Add release task about removing unsupported release version of CAPI

Signed-off-by: Chirayu Kapoor <chirayu.kapoor@suse.com>

docs/release/release-tasks.md

@@ -120,6 +120,7 @@ This comes down to changing occurrences of the old version to the new version, e
       Please note that both `InitWithKubernetesVersion` and `WorkloadKubernetesVersion` should be the highest mgmt cluster version supported by the respective Cluster API version.
 2. Update `create-local-repository.py` and `tools/internal/tilt-prepare/main.go`: `v1.4.99` => `v1.5.99`.
 3. Make sure all tests are green (also run `pull-cluster-api-e2e-full-main` and `pull-cluster-api-e2e-workload-upgrade-1-23-latest-main`).
+4. Remove unsupported release version of Cluster API. For example remove `v1.3` while working on `v1.6`.
 
 Prior art: