Remove "mphys_" prefix from files, classes, and methods.

[joanibal]

Python already provides a clear way of using namespaces through modules.
As a result the mphys_ prefix for files, classes, and methods used in the mphys module is redundant.

I propose removing the mphys_ prefix present throughout the code within the mphys repo. Although, for files like mphys_adflow.py which will eventually be moved back to the main code repo I think it does make sense to keep the prefix since it will be moved outside of the module eventually.

[JustinSGray]

this is a tough subject. Python does have name-spacing, but because you inherit from Group/Component its not always inherantly clear if a method is part of the base OpenMDAO API or part of the mphys additions.

This issue came up a lot in the OAS work. My opinion is that there is some real value in making a clear distinction between mphys methods, and standard OM methods...