Remove all_fields:true in favour of fields:*

[jpountz]

all_fields only exists because fields:* queries some fields that are not suitable for querying, and the query ultimately fails with a weird exception. We should fix fields:* to do the right thing and remove the all_fields option.

[Bargs]

This would be a tremendous help for me in elastic/kibana#12624, currently I can only generate a query against all fields by abusing the query_string query.

[jpountz]

Discussed in FixitFriday. Let's do it!