core: refactor `get_proc_name`

`get_proc_name` code is clogged with procedure cache management logic:
refactor this logic out.

Needed for #4002

NO_DOC=refactoring
NO_CHANGELOG=refactoring

Co-authored-by: Egor Elchinov <elchinov.es@gmail.com>
Co-authored-by: Georgiy Lebedev <g.lebedev@tarantool.org>