remove classification of endothelium from under epithelium

[dosumis]

This has already been done for the cell types in CL.

obophenotype/cell-ontology#1492

See this ticket for discussion

As for CL, there are some cases where we are getting automated classifications that are counter-intuitive for users.

[dosumis]

This is a little more challenging than the CL equivalent.
I think that general class will need to move to under 'tissue' - or maybe we could have a new grouping - epithelial-like?

[cmungall]

Some original discussion here:

• Endothelial development terms need relocation geneontology/go-ontology#8838

however, this left things in a confusing state. The GO discussion ended up supporting @dosumis's proposal - but at the same time GO delegated to Uberon/CL, which continued to say endo is-a epi.

I was sure we had an issue in this tracker where we discussed this in some detail, and decided that endo is-a epi... but I cannot find this!

FWIW

• ZFA has some implicit endo is-a epi classifications, but not consistent
• EMAPA does not
• FMA treats endo as (meso)epi