Generator: further refinements to the generated C code

[agarny]

• [x] For an algebraic model, we don't need to define the VariableInfo structure (this was an oversight on my part in #901).
• [x] In C, to cast the output of malloc() is redundant (see here). To cast would normally allow our generated C code to be compilable by a C++ compiler, but then again any decent C++ compiler would complain our use of malloc()/free(). So, we may as well stick to the C standard.

[nickerso]

I'm not completely convinced about removing the casting of malloc(). Have we tested that our traditional LLVM-based dynamic compilation of the generated code is happy with that?

[agarny]

I tried it in OpenCOR. I normally treat warnings as errors and neither

double * createVariablesArray()
{
    return (double *) malloc(3*sizeof(double));
}

nor

double * createVariablesArray()
{
    return malloc(3*sizeof(double));
}

can be compiled. However, if I don't treat warnings as errors, then both can be compiled just fine.

So, yes, it's all fine and the suggested change means that the code respect the C standard even more.