[repository] drop usage of no more necessary eschema_eid function
since the previous cset, we are guaranteed that repository's entity schema will
have their eid attribute properly set, so we don't have anymore to check
everytime if some entity schema's .eid attributes is set or not (and retrieve it
if not).
Related to #10450092
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/html/index.html
Files: /usr/share/doc/cubicweb-documentation/html/*