Revert "doc: enable figures enumeration" cause numfig is too slow

[marc-hb]

This reverts commit 4516117.

A git bisect showed that the duration of an incremental build doubled
after this commit enabled numfig=True. Measurements shared and
discussed in #37572, #55708 and #56631 confirmed this. Here are yet more
measurements below in two different system configurations building docs
for very recent Zephyr commit b10817b + all :numref: removed by
the previous commit. In other words these numbers show the cost of
numfig=True without even using :numref:.

• Ubuntu 22, 8 cores
  sphinx-build --version 4.3.2

time make -C doc/ html-fast

                           numfig=True   numfig=False

- from scratch             7 min 15 s       6 min 40 s

- one-line .rst change           48 s             24s

• Current Arch Linux, 72 cores
  sphinx-build --version 6.2.1

                           numfig=True   numfig=False

- from scratch              5 min 0 s      4 min 50 s

- one-line .rst change           37 s            18 s

Signed-off-by: Marc Herbert [email protected]

[marc-hb]

I just took @gmarull 's commit as is from #56631. Will pay more attention to it now, thanks for the reviews.

fixed

[Thalley]

@marc-hb Not opposing this change, but have you/we considered just omitting numfig for PRs, but keep it in for "release build documentation"?

[marc-hb]

@marc-hb Not opposing this change, but have you/we considered just omitting numfig for PRs, but keep it in for "release build documentation"?

This change does not help PRs that much actually because they build from scratch too. It's all about incremental build / iterative, local .rst compilation.

I think your idea is still valid and in fact this is more or less what I tried in #55708 but I believe the consensus there was "let's keep it simple and just get rid of numfig, it's not even that useful".

BTW I intend to return to #55708 once the numfig dust settles down because 55708 was not just about numfig.