Remove code dealing with NONMEM parsing

[MikeKSmith]

Code was introduced in MSToolkit v2 to parse NONMEM $PRED statements for use in defining the RESP function. I suggest removing this code - other tools are emerging which will enable users to translate PKPD and disease models into code for simulation (see simulx, PKPDSim, RxODE etc.). This would clean up the implementation of MSToolkit.