Remove ignore_above setting when not indexing field

[ebeahan]

Certain ECS fields are type keyword but are also not:

• searchable (index: false)
• used in aggregations, sorting, or scripting (doc_values: false)

The ECS tooling's behavior is to set ignore_above: 1024 for all keyword fields.

However, ignore_above should not be present when index: false and doc_values: false are set on a field.

[ebeahan]

Identified in elastic/kibana#101232 (comment) and discussed further in elastic/elasticsearch#74121 (comment)