Delete MeSH tree number xrefs

Delete MeSH tree number xrefs that could not be mapped to unique IDs.
If applied, this commit will fix #698.

src/ontology/uberon-edit.obo

@@ -6612,7 +6612,6 @@ xref: EMAPA:32837
 xref: FMA:61842
 xref: http://braininfo.rprc.washington.edu/centraldirectory.aspx?ID=255 {source="BIRNLEX:963"}
 xref: MA:0000924
-xref: MESH:A08.186.211.577.750
 xref: UMLS:C0752060 {source="BIRNLEX:963"}
 is_a: UBERON:0002020 ! gray matter
 relationship: part_of UBERON:0001869 ! cerebral hemisphere
@@ -17020,7 +17019,6 @@ xref: FMA:15711
 xref: GAID:312
 xref: galen:Anus
 xref: MA:0000331
-xref: MESH:A03.492.411.495.767.288
 xref: NCIT:C43362
 xref: OpenCyc:Mx4rvVjaEZwpEbGdrcN5Y29ycA
 xref: SCTID:181262009
@@ -17704,7 +17702,6 @@ synonym: "os innominatum" RELATED LATIN [Wikipedia:Hip_bone]
 synonym: "pelvic bone" EXACT [FMA:16585]
 xref: FMA:16585
 xref: GAID:205
-xref: MESH:A02.835.232.611
 xref: SCTID:361776002
 xref: Wikipedia:Hip_bone
 is_a: UBERON:0010428 {source="FMA"} ! flat bone
@@ -35137,7 +35134,6 @@ xref: http://braininfo.rprc.washington.edu/centraldirectory.aspx?ID=300 {source=
 xref: MA:0000179
 xref: MAT:0000109
 xref: MBA:549
-xref: MESH:A08.186.211.730.385.826
 xref: MIAA:0000109
 xref: NCIT:C12459
 xref: OpenCyc:Mx4rwMPQ65wpEbGdrcN5Y29ycA
@@ -104946,7 +104942,6 @@ name: fetal membrane
 def: "The amnion and chorion which surround and protect a developing fetus." [Wikipedia:Fetal_membrane]
 synonym: "adnexa fetalia" RELATED LATIN []
 xref: BTO:0000473
-xref: MESH:A16.254.403
 xref: SCTID:325510007
 xref: Wikipedia:Fetal_membrane
 is_a: UBERON:0005631 ! extraembryonic membrane
@@ -154877,7 +154872,6 @@ name: hydrophid venom
 def: "Venoms of sea snakes, Hydrophiinae, found around Pacific islands. The venoms contain fewer enzymes and more neuro- or myotoxins than land snakes. The neurotoxic proteins are similar to elapid small, short, or type I neurotoxins, some of which have been characterized." [MESH:D24.185.965.850.480]
 synonym: "hydrophid venom" RELATED [MESH:D24.185.965.850.480]
 synonym: "sea snake venom" RELATED [MESH:D24.185.965.850.480]
-xref: MESH:D24.185.965.850.480
 is_a: UBERON:0013076 {source="MESH"} ! snake venom
 
 [Term]
@@ -164158,7 +164152,6 @@ name: cysticercus stage
 def: "The larval form of any of the Taenia tapeworms." [BTO:0003168, http://www.medterms.com/]
 synonym: "cysticercus" EXACT [BTO:0003168]
 xref: BTO:0003168
-xref: MESH:B01.500.736.215.895.286
 is_a: UBERON:0000105 ! life cycle stage
 relationship: only_in_taxon NCBITaxon:6157 ! Platyhelminthes
 relationship: part_of UBERON:0000069 ! larval stage
@@ -173494,7 +173487,6 @@ id: UBERON:0018391
 name: chemoreceptor
 def: "A sensory receptor that detects chemical stimulus within the body." [http://orcid.org/0000-0002-6601-2165]
 xref: FMA:85604
-xref: MESH:A08.800.550.700.120
 is_a: UBERON:0018389 {source="FMA"} ! interoceptor
 intersection_of: UBERON:0012451 ! sensory receptor
 intersection_of: capable_of GO:0050907 ! detection of chemical stimulus involved in sensory perception