LALSimInspiral: fix documentation for 2 functions not showing up in html output

@sebastian-khan @riccardo-sturani when you go to here on the LALSimInspiral documentation you'll notice missing text for the two conversion functions:

-XLALSimInspiralTransformPrecessingNewInitialConditions() was added to an otherwise unused group and hence its detailed doc not showing up

-XLALSimInspiralTransformPrecessingWvf2PE() was showing some random comments instead of the main info

While I'm sure more could be improved about the doxygen formatting in this file, this MR makes a minimal change where it seems the output is improved enough to make the text that is in the file actually show up on the doxygen-generated htmls. To get this, I removed the 'offending' group definition, but if it was having an intended effect for some other doc output, do let me know and I'm sure it can be solved separately.

I also checked with Seb about the 'UNREVIEWED' comment that's in there, and he'll investigate.

I'll put a link and/or screenshot to the newly generated page once the pipeline goes through.