Check what usage of "get_callable_run_method" we need and what to eliminate

[ca11mejane]

Because I removed the RUN_METHOD_ALIAS constant, there is a question of which functions/methods we need to keep and what to get rid of.

need to decide on these usages:

1. ml-pipeline-engine/ml_pipeline_engine/dag_builders/annotation/builder.py

   Line 53 in cc2a0d0

   obj = get_callable_run_method(obj)

2. ml-pipeline-engine/ml_pipeline_engine/dag_builders/annotation/builder.py

   Line 97 in cc2a0d0

   node = get_callable_run_method(node)

3. ml-pipeline-engine/ml_pipeline_engine/dag_builders/annotation/builder.py

   Line 266 in cc2a0d0

   method = get_callable_run_method(self._node_map[source])

4. ml-pipeline-engine/ml_pipeline_engine/dag_builders/annotation/builder.py

   Line 292 in cc2a0d0

   if inspect.iscoroutinefunction(get_callable_run_method(node)):

I still have a question for this method. If we remove the ability to use different names in subclasses, I guess that we actually don't need to remain logic with a method's name as a string. We can just leave the abstract method "process" and use it. It will help understand codebase much faster and less painfully because the method is more explicit than the string name of the method

Originally posted by @Moootya in #33 (comment)