Remove DocumentParserContext#removeLastIgnoredField(...)

[martijnvg]

This is no longer needed as offsets of leaf array fields are stored in a doc values offset field that is controlled by field mapper.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[jordan-powers]

Will this create issues with BWC since indices with IndexVersion <= SYNTHETIC_SOURCE_STORE_ARRAYS_NATIVELY_NUMBER(9_016_0_00) still use ignored source instead of recording offsets?

[martijnvg]

Will this create issues with BWC since indices with IndexVersion <= SYNTHETIC_SOURCE_STORE_ARRAYS_NATIVELY_NUMBER(9_016_0_00) still use ignored source instead of recording offsets?

What happens is the with this change indices created before that version will just no longer use this optimization. In that case they will fallback using ignored source even if the array has just one element. I don't think this change will break anything, just disables the optimization for indices created before that version. Just to be sure I will check whether this bwc scenario is tested and if not I will add a test.

[jordan-powers]

Ah, didn't realize this was just an optimization being removed. This makes sense then, thanks!