Remove Old RT code

[riclarsson]

Once DOIT has been updated (#207), a lot of the old RT code becomes obsolete. I will have a look at removing it. Please ping me @m-brath when you are done with #207 .

[m-brath]

@riclarsson The old DOIT and my new DOIT are using only one function of rte.{cc,h}. Both use the "get_iy" - function to get the incoming radaition on the cloudbox, which is an interface to iy_main_agenda that can be used if only iy is of interest. For the case of old DOIT the "get_iy" - function can be moved to doit.{cc,h}. For the case of my new DOIT, I would include this function within my newdoit files.

[erikssonpatrick]

This is good news. This is just a small helper function that is independent of the change to the "new RT" system.

Not critical, but it could be considered to remove get_iy and instead call iyCalc.