[6.6] Remove ECS aliases

[graphaelli]

reverts most of #1609, part of #1670, and all of #1665.

aliases that remain are inherited from libbeat processors:

# Common Beats fields
- name: event.timezone
  path: beat.timezone

# Cloud processor fields
- name: cloud.provider
  path: meta.cloud.provider
- name: cloud.instance.id
  path: meta.cloud.instance_id
- name: cloud.instance.name
  path: meta.cloud.instance_name
- name: cloud.machine.type
  path: meta.cloud.machine_type
- name: cloud.availability_zone
  path: meta.cloud.availability_zone
- name: cloud.project.id
  path: meta.cloud.project_id
- name: cloud.region
  path: meta.cloud.region

# Docker processor fields
- name: container.id
  path: docker.container.id
- name: container.name
  path: docker.container.name
- name: container.image.name
  path: docker.container.image

closes #1794

will need a backport to 6.x

[simitt]

jenkins, retest this please

[graphaelli]

jenkins, retest this please

[simitt]

Why are we aliasing this field and not including it in the reindexing script? And shouldn't beat.hostname go to observer.hostname?

[graphaelli]

Sorry, this is confusing. This doesn't create an alias, it's just beats' log of their aliases. The only aliases that are actually created are listed in the description.