read_view: remove activate logic

A read view must be activated in the thread that's going to use it.
This is required to support space upgrade and tuple format, which are
only used in EE. "Raw" index read view methods (returning raw message
pack data) don't require any activation by design so let's move read
view activate/deactivate logic completely to the EE repository.

Needed for https://github.com/tarantool/tarantool-ee/issues/247

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring