Get rid of eglot--obj, an uninteresting abstraction

Get rid of eglot--obj, an uninteresting abstraction

* eglot.el (eglot--obj): Get rid of this. It wasn't widely used
anyway.
(eglot-client-capabilities)
(eglot--connect, eglot--async-request, eglot--notify)
(eglot--reply, eglot--pos-to-lsp-position, eglot-handle-request)
(eglot--register-unregister, eglot-handle-request)
(eglot--TextDocumentIdentifier)
(eglot--VersionedTextDocumentIdentifier)
(eglot--TextDocumentItem, eglot--TextDocumentPositionParams)
(eglot--signal-textDocument/didChange)
(eglot--signal-textDocument/didSave)
(xref-backend-identifier-completion-table)
(xref-backend-references, xref-backend-apropos, eglot-imenu)
(eglot-rename): Use list instead of eglot--obj.