Remove duplicate writing of datasets

Hey @j2b.bayle, I think I encountered a tiny bug: test mass (carriers + usbs) and reference (carriers + usbs) are written twice to the HDF5 file, i.e. in instrument.py the lines 1765, 1768, 1773, 1776 are identical to the lines 1781, 1782, 1783, 1784. This leads to the error ‘Unable to create dataset (name already exists)’.

I deleted those datasets in the blocks where the offsets and fluctuations are written to the file and kept them in the block where the total beat notes are written to the file. Is that ok?