Better flag documentation. (#28753)

sdks/python/apache_beam/runners/dataflow/dataflow_runner.py

@@ -97,10 +97,6 @@ def __init__(self, cache=None):
   def is_fnapi_compatible(self):
     return False
 
-  def apply(self, transform, input, options):
-    _check_and_add_missing_options(options)
-    return super().apply(transform, input, options)
-
   @staticmethod
   def poll_for_job_completion(
       runner, result, duration, state_update_callback=None):
@@ -496,10 +492,6 @@ def _get_coder(typehint, window_coder):
           coders.registry.get_coder(typehint), window_coder=window_coder)
     return coders.registry.get_coder(typehint)
 
-  # TODO(srohde): Remove this after internal usages have been removed.
-  def apply_GroupByKey(self, transform, pcoll, options):
-    return transform.expand(pcoll)
-
   def _verify_gbk_coders(self, transform, pcoll):
     # Infer coder of parent.
     #
@@ -589,12 +581,14 @@ def _check_and_add_missing_options(options):
   sdk_location = options.view_as(SetupOptions).sdk_location
   if 'dev' in beam.version.__version__ and sdk_location == 'default':
     raise ValueError(
-        "When launching Dataflow Jobs with an unreleased SDK, "
+        "You are submitting a pipeline with Apache Beam Python SDK "
+        f"{beam.version.__version__}. "
+        "When launching Dataflow jobs with an unreleased (dev) SDK, "
         "please provide an SDK distribution in the --sdk_location option "
-        "to use consistent SDK version at "
-        "pipeline submission and runtime. To ignore this error and use the "
-        "SDK installed in Dataflow dev containers, use "
-        "--sdk_location=container.")
+        "to use a consistent SDK version at "
+        "pipeline submission and runtime. To ignore this error and use "
+        "an SDK preinstalled in the default Dataflow dev runtime environment "
+        "or in a custom container image, use --sdk_location=container.")
 
   # Streaming only supports using runner v2 (aka unified worker).
   # Runner v2 only supports using streaming engine (aka windmill service)