Simplify geo_factors_codegen w/ skip_dir_nesting

[bradley-solliday-skydio]

Previously, geo_factors_codegen.py was using an ad-hoc system of
generating all the C++ factors into a factors folder. It did this by
calling Codegen.generate_function to generate the code into a
temporary file, read the file into a string, then re-wrote the string
into the desired location. I assume this was to avoid all the fluff
that's generated by default with Codegen.generate_function.

However, there is the skip_directory_nesting optional argument for
Codegen.generate_function which does precisely that (I think the code
in this file might have been written before that option was added).

So, to reduce confusion (such as the confusion I faced when I first
started looking at this file) and complexity, I rewrote the code to
instead use the skip_directory_nesting argument.

Topic: geo_factors_use_skip_directory_nesting

[bradley-solliday-skydio]

Reviews in this chain:
└#292 Simplify geo_factors_codegen w/ skip_dir_nesting
　└#294 Add diagonal & isotropic sqrt_infos in geo factors

[bradley-solliday-skydio]

#	head	base	diff	date	summary
0	f9a6f2d0	4c368815	diff	Jan 17 17:19 PM	1 file changed, 13 insertions(+), 56 deletions(-)

[aaron-skydio]

However, there is the skip_directory_nesting optional argument for
Codegen.generate_function which does precisely that (I think the code
in this file might have been written before that option was added).

Yep exactly, this predates skip_directory_nesting :)

Thanks for cleaning up!