ZFA's 'griseum centrale' (ZFA:0000518) is mapped to Uberon's 'central
gray substance of midbrain' (UBERON:0003040).

This is likely incorrect as the ZFA term refers to a structure that is
part of the hindbrain, whereas the Uberon term refers to a midbrain
structure.

The correct mapping is most likely 'central gray substance of medulla'
(UBERON:0002867), which is part of the hindbrain.

partially addresses #3353

ZFA's 'coelom' (ZFA:0001438) is mapped to Uberon's 'coelemic cavity
lumen' (UBERON:0002323).

This is incorrect as the ZFA terms refers to a multi-tissue structure
and therefore to a material entity, whereas the Uberon term refers to
the anatomical cavity *within* the coelom (an immaterial entity).

Uberon has another term to refer to the (material) anatomical structure
that forms the coelemic cavity: 'coelom' (UBERON:0011997), the ZFA term
should be mapped to that term instead.

partially addresses #3353

ZFA's 'inferior raphe nucleus' (ZFA:0000366) is mapped to Uberon's
'dorsal raphe nucleus' (UBERON:0002043).

This is likely wrong for at least two reasons:

* the ZFA term refers to a nucleus that is part of the hindbrain,
  whereas the Uberon term refers to a nucleus that is part of the
  midbrain;
* according to Beecher, Beamer & Bartlett 2019 [1], the 'dorsal raphe
  nucleus' is one of the *superior* raphe nuclei, which makes it
  doubtful, even considering possible terminological differences across
  species, that it should be mapped to an *inferior* raphe nucleus.

The same reference states that the 'inferior raphe nucleus' is a complex
comprising the following nuclei:

* the 'nucleus raphe obscurus' (UBERON:0002684),
* the 'nucleus raphe pallidus' (UBERON:0002157),
* and the 'nucleus raphe magnus' (UBERON:0002156).

In Uberon, those three nuclei are the parts that make up the 'medullary
raphe nuclear complex' (UBERON:0002692), leading me to believe that this
complex is in fact what ZFA (along with Beecher, Beamer, & Bartlett)
calls the 'inferior raphe nucleus'.

So here, we remap ZFA's 'inferior raphe nucleus' to 'medullary raphe
nuclear complex', and also add a 'inferior raphe nuclei' synonym to the
Uberon term.

closes #3356

[1] doi:10.1016/B978-0-12-800050-2.00006-1

We had re-mapped ZFA:0000366 ('inferior raphe nucleus') from
UBERON:0002043 ('dorsal raphe nucleus') to UBERON:0002692 ('medullary
raphe nuclear complex'), which seemed a better match.

However, for lack of certainty about what the ZFA term really
represents, it is better to drop the mapping entirely.

There are conflicting statements in the available literature regarding
the mammalian equivalent of ZFA's 'griseum centrale'.

Candidates include:

* the 'central gray substance of midbrain' (aka the 'periaqueductal
  gray'), according to Olson et al. 2024
  (doi:10.1016/j.ibror.2017.01.001);
* the 'nucleus incertus', according to Spikol et al. 2024
  (doi:10.7554/eLife.89516.3);
* and the 'central gray substance of medulla', based on the
  classification of the ZFA term.

It is better to simply remove the mapping for now.