Bring GBn2 into the simtk.openmm.app namespace. Also remove some redundant

references.

wrappers/python/simtk/openmm/app/__init__.py

@@ -15,7 +15,7 @@ from pdbfile import PDBFile
 from forcefield import ForceField
 from simulation import Simulation
 from pdbreporter import PDBReporter
-from amberprmtopfile import AmberPrmtopFile
+from amberprmtopfile import AmberPrmtopFile, HCT, OBC1, OBC2, GBn, GBn2
 from amberinpcrdfile import AmberInpcrdFile
 from dcdfile import DCDFile
 from gromacsgrofile import GromacsGroFile
@@ -37,8 +37,3 @@ PME = forcefield.PME
 HBonds = forcefield.HBonds
 AllBonds = forcefield.AllBonds
 HAngles = forcefield.HAngles
-
-HCT = amberprmtopfile.HCT
-OBC1 = amberprmtopfile.OBC1
-OBC2 = amberprmtopfile.OBC2
-GBn = amberprmtopfile.GBn