[Fleet] Clean up legacy elasticsearch imports

[jen-huang]

There are two remaining elasticsearch imports in Fleet:

kibana/x-pack/plugins/fleet/server/errors/handlers.ts

Line 10 in e1e93eb

import { errors as LegacyESErrors } from 'elasticsearch';

kibana/x-pack/plugins/fleet/server/errors/handlers.test.ts

Line 9 in e1e93eb

import { errors } from 'elasticsearch';

These should be removed or replaced with types from /src/core/types/elasticsearch.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)