SimParams: less boilerplate

The code look as if it was trying to prevent direct instantiation of the
SimParams class. However, instance *creation* in Python is actually
handled via `__new__` which was not overridden. In addition, the
`get()` accessor was invoking `SimParams.__new__()` directly, which
meant that this class was instantiated each time it was needed.

Let's cut the boilerplate by getting rid of the extra step and just use
the regular constructor.

This patch doesn't change anything in actual observable behavior. I
still do not like this implicit singleton design pattern, but nuking
that will have to wait until some other time.

Change-Id: I3ca81bcd0042e91b4f6b7581879922611f18febe

gnpy/core/science_utils.py

@@ -24,7 +24,7 @@ from gnpy.core.parameters import SimParams
 from gnpy.core.info import SpectralInformation
 
 logger = getLogger(__name__)
-sim_params = SimParams.get()
+sim_params = SimParams()
 
 def raised_cosine_comb(f, *carriers):
     """ Returns an array storing the PSD of a WDM comb of raised cosine shaped