fix: raise error on import of AsyncPipeline (#178)

* raise error for async import
* Remove all async pipeline tests

Author: Amnah199

haystack_experimental/__init__.py

@@ -2,4 +2,4 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-from .core import Pipeline, AsyncPipeline, run_async_pipeline
+from .core import AsyncPipeline, Pipeline

haystack_experimental/core/__init__.py

@@ -2,7 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-from .pipeline import AsyncPipeline, run_async_pipeline
 from .pipeline import Pipeline
+from .pipeline.async_pipeline import AsyncPipeline
 
-_all_ = ["AsyncPipeline", "run_async_pipeline", "Pipeline"]
+_all_ = ["Pipeline"]

haystack_experimental/core/pipeline/__init__.py

@@ -2,7 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-from .async_pipeline import AsyncPipeline, run_async_pipeline
+from .async_pipeline import AsyncPipeline
 from .pipeline import Pipeline
 
-__all__ = ["AsyncPipeline", "run_async_pipeline", "Pipeline"]
+__all__ = ["Pipeline"]