Remove injections about RO:has_skeleton.

In RO, 'has skeleton' (RO:0002551) is domain-restricted to 'anatomical
structure' (UBERON:0000061) and range-restricted to 'material anatomical
entity' (UBERON:0000465).

Currently, in Uberon we are overriding those restrictions by injecting
tigher constraints: a domain restriction to 'organism subdivision'
(UBERON:0000475) and a range restriction to 'subdivision of skeleton'
(UBERON:0010912).

A ticket to upstream those tighter restrictions to RO has gone nowhere
in more than one year
(oborel/obo-relations#700).

This PR removes the Uberon-injected restrictions and leaves it to RO to
decide whether they should adopt them or not.

Of note, the only inferred axiom that those tighter restrictions give us
is this one:

> 'nose' SubClassOf: 'organism subdivision'

So we don't lose much by removing them until they are (maybe) added back
directly by RO.

Related to #2453

src/ontology/uberon-edit.obo

@@ -225264,8 +225264,6 @@ is_metadata_tag: true
 id: has_skeleton
 name: has skeleton
 xref: RO:0002551
-domain: UBERON:0000475 ! organism subdivision
-range: UBERON:0010912 ! subdivision of skeleton
 
 [Typedef]
 id: has_start