box: drop field max_id in space _schema

Now we use _space:max() instead of max_id for space id generation, so
it is not used anymore. The patch removes max_id from bootstrap snapshot,
adds upgrade and downgrade scripts.

Closes #5997

@TarantoolBot document
Title: Update the description of _schema
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/_schema/

Since tarantool 2.11.1, there is no max_id field in space _schema.