Remove backcompat code for stackdriver (#36442)

Remove back-compatibility code for stackdriver now that we are
at >= 2.6.0.

This caused problems recently with flaky / leaking tests but
hopefully #36455 fixed the triggering mechanism for that flaky
test and this one should succeed now.

airflow/providers/google/cloud/log/stackdriver_task_handler.py

@@ -30,21 +30,13 @@
 
 from airflow.providers.google.cloud.utils.credentials_provider import get_credentials_and_project_id
 from airflow.providers.google.common.consts import CLIENT_INFO
+from airflow.utils.log.trigger_handler import ctx_indiv_trigger
 
 if TYPE_CHECKING:
-    from contextvars import ContextVar
-
     from google.auth.credentials import Credentials
 
     from airflow.models import TaskInstance
 
-try:
-    # todo: remove this conditional import when min airflow version >= 2.6
-    ctx_indiv_trigger: ContextVar | None
-    from airflow.utils.log.trigger_handler import ctx_indiv_trigger
-except ImportError:
-    ctx_indiv_trigger = None
-
 DEFAULT_LOGGER_NAME = "airflow"
 _GLOBAL_RESOURCE = Resource(type="global", labels={})