Remove support for fractional byte size values

[jasontedor]

These have been deprecated since Elasticsearch 6.2.0. This commit finishes them off by removing support for parsing them.

Relates #27702

[elasticmachine]

Pinging @elastic/es-core-infra (:Core/Infra/Core)

[cjcenizal]

@jasontedor The underlying issue (#27568) has this to say about handling the change in 7.0:

Auto-upgrade cluster and index settings from LegacyByteSizeValue to ByteSizeValue (the new one) and remove LegacyByteSizeValue. Fractional bytes values in elasticsearch.yml will need to be manually changed by the user when upgrading to 7.0 or can be changed before upgrading.

I might be confused, but the issue also notes that this change affects not only settings but API parameters that are byte values as well. Do we need to consider the upgrade path for any documents created with fractional byte size values? For example, an ILM policy with fractional byte size values? Or is this what was meant by "index settings"?

[jasontedor]

I might be confused, but the issue also notes that this change affects not only settings but API parameters that are byte values as well. Do we need to consider the upgrade path for any documents created with fractional byte size values? For example, an ILM policy with fractional byte size values? Or is this what was meant by "index settings"?

Documents are not an issue since we don't have any mappers that parse byte size values today. The upgrade issue only pertains to:

• cluster settings
• index settings
• cluster state metadata that uses byte size values (e.g., an ILM policy)

The work to automatically upgrade these was suppose to have been done as part of the 7.0.0 work, but it appears it was not so we are left with this legacy for another major release. To complete this work, we have to do the following:

• add code to upgrade any byte size setting in the cluster state; we have infrastructure for this
• add code to upgrade any byte size setting in an index; we have infrastructure for this
• add code to all cluster state metadata to be upgraded; we don't have infrastructure for this

Given that we are not ready (as I thought since #27568 is closed), I will close this pull request for now.