Mark synonyms as abbreviations where appropriate.

Since STG is an abbreviation for "stomatogastric ganglion", it is more
appropriate to make it a RELATED synonym (rather than an EXACT synonym),
and to explicitly flag it with the "abbreviation" (OMO:0003000) synonym
type (as per the Uberon editor SOP).

Likewise for similar abbreviations on crustacean nerves.

src/ontology/uberon-edit.obo

@@ -224769,7 +224769,7 @@ relationship: in_taxon NCBITaxon:6656 ! Arthropoda
 id: UBERON:8910001
 name: stomatogastric ganglion
 def: "The stomatogastric ganglion (STG) consists of about 30 neurons that form two central pattern generator circuits in crustaceans. STG neurons have large soma (~50-100 um) and have complex branches. The STG contains the motor neurons that innervate the striated muscles that move the gastric mill and pyloric regions of the stomach." [PMID:17009928]
-synonym: "STG" EXACT [PMID:17009928]
+synonym: "STG" RELATED OMO:0003000 [PMID:17009928]
 is_a: UBERON:0011216 ! organ system subdivision
 relationship: dc-contributor https://orcid.org/0000-0002-1909-7004
 relationship: in_taxon NCBITaxon:6692 ! Pleocyemata